Dressing and apparatus for cleansing the wounds

ABSTRACT

A dressing ( 2 ) and an apparatus ( 1 ) comprising the dressing, for cleansing the wounds ( 5 ) in which an irrigant fluid from a reservoir ( 12 ) connected to a conformable would dressing and would exudate from the dressing are moved by a device ( 18 ) (which may be a single pump or two pumps) for moving fluid through a flow Path ( 6, 7, 9, 10 ) which passes through the dressing with a means for providing simultaneous aspiration and irrigation of the wound, to provide a desired balance of fluid at a controlled nominal flow rate that removes materials deleterious to wound healing, while distributing materials that are beneficial in promoting would healing over the would bed.

The present invention relates to apparatus and a medical wound dressingfor aspirating, irrigating and/or cleansing wounds, and a method oftreating wounds using such apparatus for aspirating, irrigating and/orcleansing wounds.

It relates in particular to such an apparatus, wound dressing and methodthat can be easily applied to a wide variety of, but in particularchronic, wounds, to cleanse them of materials that are deleterious towound healing, whilst distributing materials that are beneficial in sometherapeutic aspect, in particular to wound healing.

Aspirating and/or irrigating apparatus are known, and tend to be used toremove wound exudate during wound therapy. In known forms of such woundtherapy, aspiration and irrigation of the wound take place sequentially.

Each part of the therapy cycle is beneficial in promoting wound healing:

Aspiration applies a negative pressure to the wound, which is beneficialin itself in promoting wound healing by removing materials deleteriousto wound healing with the wound exudate, reducing bacterial load,combating peri-wound oedema, increasing local blood flow to the woundand encouraging the formation of wound bed granulation tissue.

Irrigation cleanses wounds of materials that are deleterious to woundhealing by diluting and moving wound exudate (which is typicallyrelatively little fluid and may be of relatively high viscosity andparticulate-filled.

Additionally, relatively little of beneficial materials involved inpromoting wound healing (such as cytokines, enzymes, growth factors,cell matrix components, biological signaling molecules and otherphysiologically active components of the exudate) are present in awound, and are not well distributed in the wound, i.e. they are notnecessarily present in parts of the wound bed where they can bepotentially of most benefit. These may be distributed by irrigation ofthe wound and thus aid in promoting wound healing.

The irrigant may additionally contain materials that are potentially oractually beneficial in respect of wound healing, such as nutrients forwound cells to aid proliferation, and gases, such as oxygen. These maybe distributed by irrigation of the wound and thus aid in promotingwound healing.

If aspiration and irrigation therapy is applied sequentially to a wound,the two therapies, each of which is beneficial in promoting woundhealing, can only be applied intermittently.

Thus, the wound will lose the abovementioned known beneficial effects ofaspiration therapy on wound healing, at least in part, while thataspiration is suspended during irrigation.

Additionally, for a given aspirate flow, whilst materials that arepotentially or actually deleterious in respect of wound healing areremoved from wound exudate, the removal in a given time period ofapplication of the total irrigate and/or aspirate therapy will normallybe less effective and/or slower than with continuous application ofaspiration.

Even less to be desired, is that while aspiration is not applied to thewound, wound exudate and materials deleterious to wound healing (such asbacteria and debris, and iron II and iron III and for chronic woundsproteases, such as serine proteases) will pool on the wound bed andhinder wound healing, especially in a highly exuding wound. The influxof local oedema will also add to the chronicity of the wound. This isespecially the case in chronic wounds.

Depending on the relative volumes of irrigant and wound exudate, themixed exudate-irrigant fluid and may be of relatively high viscosityand/or particulate-filled. Once it is present and has pooled, it may bemore difficult to shift by the application of aspiration in aconventional sequential aspirate—irrigate—dwell cycle than withcontinuous simultaneous aspiration of the wound, owing to the viscosityand blockage in the system.

The wound will also lose the abovementioned beneficial effects ofirrigation therapy on wound healing, at least in part, while thatirrigation is suspended during aspiration.

These benefits in promoting wound healing include the movement ofmaterials that are beneficial in promoting wound healing, such as thosementioned above.

Additionally, for a given irrigant flow, the cleansing of the wound andthe distribution by irrigation of the wound of such beneficial materialsin a given time period of application of the total irrigate and/oraspirate therapy when such therapy is in a conventional sequentialaspirate—irrigate—dwell cycle will normally be less effective and/orslower than with continuous application of aspiration.

Such known forms of aspiration and/or irrigation therapy systems alsooften create a wound environment that may result in the loss of optimumperformance of the body's own tissue healing processes, and slow healingand/or in weak new tissue growth that does not have a strongthree-dimensional structure adhering well to and growing from the woundbed.

This is a significant disadvantage, in particular in chronic wounds.

The relevant devices tend not to be portable.

It thus would be desirable to provide a system of aspiration andirrigation therapy for a wound, which

-   can remove wound exudate and materials deleterious to wound healing    from contact with the wound bed,-   whilst simultaneously cleansing it and distributing materials that    are beneficial in promoting wound healing across it.

It is an object of the present invention to obviate at least some of theabovementioned disadvantages of known aspiration and/or irrigationtherapy systems.

It is a yet further object of the present invention

-   a) to obviate at least some of the abovementioned disadvantages of    known aspiration and/or irrigation systems, and-   b) is portable.

Vascular supply to, and aspiration in, tissue underlying and surroundingthe wound is often compromised.

It is a further object of the present invention to provide a system oftherapy that also promotes vascular supply to tissue underlying andsurrounding a wound, promoting wound healing.

Thus, according to a first aspect of the present invention there isprovided an apparatus for aspirating, irrigating and/or cleansingwounds, comprising

-   a) a fluid flow path, comprising a conformable wound dressing,    having a backing layer which is capable of forming a relatively    fluid-tight seal or closure over a wound and    -   at least one inlet pipe for connection to a fluid supply tube,        which passes through and/or under the wound-facing face, and    -   and at least one outlet pipe for connection to a fluid offtake        tube, which passes through and/or under the wound-facing face,    -   the point at which the or each inlet pipe and the or each outlet        pipe passes through and/or under the wound-facing face forming a        relatively fluid-tight seal or closure over the wound;-   b) a fluid reservoir connected by a fluid supply tube to an inlet    pipe via optional means for supply flow regulation;-   c) at least one device for moving fluid through the wound dressing;    characterised in that it comprises-   d) means for providing simultaneous aspiration and irrigation of the    wound, such that fluid may be supplied to fill the flowpath from the    fluid reservoir via the fluid supply tube (optionally via means for    supply flow regulation) while fluid is aspirated by a device through    the fluid offtake tube (optionally or as necessary via means for    aspirate flow regulation).

Where any pipe is described in connection with the apparatus as beingconnected or for connection to a (mating end of a) tube, e.g. a fluidsupply tube or fluid offtake tube, the pipe and the tube may form asingle integral unit in the flow path.

The present invention in this aspect provides several advantages.

One is that application of an irrigant to a wound under simultaneousaspiration creates a wound environment that is exposed to the continuousbeneficial effects of both aspects of the therapy for wound healing, asopposed to the sequential intermittent application of irrigant flow andaspiration in known aspirating and/or irrigating apparatus. The latterresult in less than optimum performance of the body's own tissue healingprocesses, and slower healing and/or weaker tissue growth that does nothave a strong three-dimensional structure adhering well to and growingfrom the wound bed. This is a significant disadvantage, in particular inchronic wounds.

Thus, the use of the apparatus of this first aspect of the presentinvention for aspirating, irrigating and/or cleansing wounds retains andenhances the beneficial effects of aspiration in respect of woundhealing by continuous and preferably constant aspiration. These includeremoving materials deleterious to wound healing with the wound exudate,reducing bacterial load, combating peri-wound oedema and encouraging theformation of wound bed granulation tissue.

Preferred embodiments of the apparatus of this first aspect of thepresent invention for aspirating, irrigating and/or cleansing chronicwounds apply a milder negative pressure than in conventional negativepressure therapy (which is too aggressive for the fragile tissues ofmany such wounds). This leads to increased patient comfort, and lessensthe risk of inflammation of the wound.

The removal of wound exudate in a given time period of application ofthe total irrigate and/or aspirate therapy will normally be moreeffective and/or faster than with a conventional sequential intermittentaspiration and/or irrigation therapy.

Even more desirably, since simultaneous aspiration and irrigation isapplied to the wound, wound exudate and materials deleterious to woundhealing (such as bacteria and debris, and iron II and iron III and forchronic wounds proteases) will not pool on the wound bed and hinderwound healing, especially in a highly exuding wound. This is especiallyimportant in chronic wounds.

The resulting mixed exudate-irrigant fluid will usually be of relativelylower viscosity.

Because simultaneous aspiration and irrigation of the wound providescontinuous removal at a constant relatively high speed, the fluid doesnot have to be accelerated cyclically from rest, and will be easier toshift than with known forms of aspiration and/or irrigation therapysystems with a conventional sequential aspirate—irrigate—dwell cycle.

This will thus exert a greater net effect on the removal of adherentbacteria and debris.

This is especially the case in those embodiments of the apparatus ofthis first aspect of the present invention for aspirating, irrigatingand/or cleansing wounds where there is an inlet manifold (as describedin further detail hereinafter) that covers and contacts most of thewound bed with openings that deliver the fluid directly to the wound bedover an extended area.

The present form of aspiration and/or irrigation therapy systems alsooften create a wound environment for better distribution of materialsthat are beneficial in some therapeutic aspect, in particular to woundhealing, that are present in a wound, but may not be well distributed inthe wound, e.g. in a highly exuding wound (These include cytokines,enzymes, growth factors, cell matrix components, biological signallingmolecules and other physiologically active components of the exudate.),and or materials contained in the irrigant such as nutrients for woundcells to aid proliferation, and gases, such as oxygen.

These may aid wound cell proliferation and new tissue growth that has astrong three-dimensional structure adhering well to and growing from thewound bed. This is a significant advantage, in particular in chronicwounds.

This is especially the case in those embodiments of the apparatus ofthis first aspect of the present invention for aspirating, irrigatingand/or cleansing wounds where there is an inlet manifold as describedbelow.

This covers and contacts most of the wound bed with openings thatdeliver the fluid directly to the wound bed over an extended area.

It will be seen that the balance of fluid between fluid aspirated fromthe wound and irrigant supplied to the wound from the irrigant reservoirmay provide a predetermined steady state concentration equilibrium ofmaterials beneficial in promoting wound healing over the wound bed.Simultaneous aspiration of wound fluid and irrigation at a controlledflow rate aids in the attainment and maintenance of this equilibrium

The apparatus for irrigating and/or aspirating wounds of the presentinvention may be used cyclically and/or with reversal of flow.

Preferably the present apparatus for aspirating, irrigating and/orcleansing wounds is a conventionally automated, programmable systemwhich can cleanse the wound with minimal supervision.

The means for providing simultaneous aspiration and irrigation of thewound often comprises

-   a (first) device for moving fluid through the wound applied to fluid    downstream of and away from the wound dressing, in combination with    at least one of-   a second device for moving fluid through the wound applied to the    irrigant in the fluid supply tube upstream of and towards the wound    dressing;-   means for aspirate flow regulation, connected to a fluid offtake    tube, and means for supply flow regulation, connected to a fluid    supply tube;

The (first) device will apply negative pressure (i.e. below-atmosphericpressure or vacuum) to the wound bed. It may be applied to the aspiratein the fluid offtake tube downstream of and away from the wounddressing.

Alternatively or additionally, where appropriate, the aspirate in thefluid offtake tube downstream of the wound dressing may be aspiratedinto a collection vessel, and the first device may act on fluid such asair from the collection vessel.

The (first) device may be a fixed-throughput device, such as afixed-speed pump, which will usually require a discrete means foraspirate flow regulation, connected to a fluid offtake tube, and/ormeans for supply flow regulation, connected to a fluid supply tube, ineach case, e.g. a regulator, such as a rotary valve.

Alternatively, where appropriate the (first) device for moving fluidthrough the wound may be a variable-throughput device, such as avariable-speed pump, downstream of the wound dressing, thus effectivelyforming a combination of a (first) device for moving fluid through thewound with means for aspirate flow regulation and/or means for supplyflow regulation in a single integral unit.

The (first) device for moving fluid through the wound will often be apump of any of the following types, or a piped supply of vacuum, appliedto fluid downstream of and away from the wound dressing. In the case ofany pump it may be a fixed-speed pump, with (as above) a discrete meansfor aspirate flow regulation, connected to a fluid offtake tube, and/ormeans for supply flow regulation, connected to a fluid supply tube, ineach case, e.g. a regulator, such as a rotary valve. Alternatively,where appropriate the pump may be a variable-throughput orvariable-speed pump.

The following types of pump may be used as the (first) device:

-   reciprocating pumps, such as piston pumps—where pistons pump fluids    through check valves, in particular for positive and/or negative    pressure on the wound bed; and-   diaphragm pumps—where pulsations of one or two flexible diaphragms    displace liquid with check valves.-   and-   rotary pumps, such as:-   progressing cavity-   pumps—with a cooperating screw rotor and stator, in particular for    higher-viscosity and particulate-filled exudate; and-   vacuum pumps—with pressure regulators.

The (first) device may be a diaphragm pump, e.g. preferably a smallportable diaphragm pump. This is a preferred type of pump, in order inparticular to reduce or eliminate contact of internal surfaces andmoving parts of the pump with (chronic) wound exudate, and for ease ofcleaning.

Where the pump is a diaphragm pump, and preferably a small portablediaphragm pump, the one or two flexible diaphragms that displace liquidmay each be, for example a polymer film, sheet or membrane, that isconnected to means for creating the pulsations. This may be provided inany form that is convenient, inter alia as a piezoelectric transducer, acore of a solenoid or a ferromagnetic integer and coil in which thedirection of current flow alternates, a rotary cam and follower, and soon.

Where any second device is applied to the fluid in the fluid supply tubeupstream of and towards the wound dressing, it will usually applypositive pressure (i.e. above-atmospheric pressure) to the wound bed.

As with the (first) device, it may be a fixed-throughput device, such asa fixed-speed pump, which will usually require a discrete means forsupply flow regulation, connected to a fluid supply tube, e.g. aregulator, such as a rotary valve.

Alternatively, where appropriate the second device for moving irrigantfluid to the wound may be a variable-throughput device, such as avariable-speed pump, upstream of the wound dressing, thus effectivelyforming a combination of a second device for moving fluid through thewound with means for supply flow regulation in a single integral unit.

The second device for moving fluid through the wound will often be apump of any of the following types applied to the irrigant in the fluidsupply tube upstream of and towards the wound dressing. It may be afixed-speed pump, with (as above) a discrete means for supply flowregulation, connected to a fluid supply tube, e.g. a regulator, such asa rotary valve. Alternatively, where appropriate the pump may be avariable-throughput or variable-speed pump.

The following types of pump may be used as the second device:

-   reciprocating pumps, such as-   shuttle pumps—with an oscillating shuttle mechanism to move fluids    at rates from 2 to 50 ml per minute-   and-   rotary pumps, such as:-   centrifugal pumps-   flexible impeller-   pumps—where elastomeric impeller traps fluid between impeller blades    and a moulded housing that sweeps fluid through the pump housing.-   peristaltic pumps—with peripheral rollers on rotor arms acting on a    flexible fluid aspiration tube to urge fluid current flow in the    tube in the direction of the rotor.-   rotary vane pumps—with rotating vaned disk attached to a drive shaft    moving fluid without pulsation as it spins. The outlet can be    restricted without damaging the pump.

The second device may be a peristaltic pump, e.g. preferably a smallportable peristaltic pump. This is a preferred type of pump, in order inparticular to reduce or eliminate contact of internal surfaces andmoving parts of the pump with irrigant, and for ease of cleaning.

Where the pump is a peristaltic pump, this may be e.g., an Instech ModelP720 miniature peristaltic pump, with a flow rate: of 0.2-180 ml/hr anda weight of <0.5 k. This is potentially useful for home and fieldhospital use.

Each such pump of any these types may also suitably be one that iscapable of pulsed, continuous, variable and/or automated and/orprogrammable fluid movement. Less usually and less preferably, each suchpump of any these types will be reversible.

As above, the means for supply flow regulation may be a regulator, suchas a rotary valve. This is connected between two parts of a fluid supplytube, such that the desired supply flow regulation is achieved.

If there are two or more inlet pipes, these may be connected to a singlefluid supply tube with a single regulator, or to first, second, etc.fluid supply tubes, respectively having a first regulator, a secondregulator, etc., e.g. a valve or other control device for admittingfluids into the wound.

As above, the means for aspirate flow regulation may be similarlyprovided in a form in which concomitant aspirate flow regulation ispossible. It may be a regulator, such as a valve or other controldevice, e.g. a rotary valve.

Multiple offtake tubes may be similarly provided with single or multipleregulators, all for aspiration of fluids from the apparatus, e.g. to aaspirate collection vessel, such as a collection bag.

If there is no second device for moving fluid through the wound appliedto the irrigant in the fluid supply tube upstream of and towards thewound dressing, it is only possible to apply a negative pressure to thewound, by means of the device for moving fluid through the wound appliedto the aspirate in the fluid offtake tube downstream of and away fromthe wound dressing.

Operation may e.g. be carried out at a negative pressure of up to 50%atm., typically at a low negative pressure of up to 20% atm., moreusually up to 10% atm. at the wound, as is described hereinafter.

Examples of suitable and preferred (first) devices include those typesof pump that are so described hereinbefore in relation to the firstdevice. This may be a diaphragm pump, e.g. preferably a small portablediaphragm pump. This is a preferred type of pump, in order in particularto reduce or eliminate contact of internal surfaces and moving parts ofthe pump with (chronic) wound exudate, and for ease of cleaning.

Alternatively, if it is desired to apply a net positive pressure to thewound, the means for providing simultaneous aspiration and irrigation ofthe wound must comprise not only

-   a first device for moving fluid through the wound applied to the    aspirate in the fluid offtake tube downstream of and away from the    wound dressing, but also-   a second device for moving fluid through the wound applied to the    irrigant in the fluid supply tube upstream of and towards the wound    dressing.

Operation may then e.g. be carried out at a positive pressure of up to50% atm., typically at a low positive pressure of up to 20% atm., moreusually up to 10% atm. at the wound, as is described hereinafter.

Examples of suitable and preferred first devices include those types ofpump that are so described hereinbefore in relation to the first device.This may be a diaphragm pump, e.g. preferably a small portable diaphragmpump.

This is a preferred type of pump, in order in particular to reduce oreliminate contact of internal surfaces and moving parts of the pump with(chronic) wound exudate, and for ease of cleaning.

Examples of suitable and preferred second devices include those types ofpump that are so described hereinbefore in relation to the seconddevice. This may be a peristaltic pump, e.g. a miniature peristalticpump.

This is a preferred type of pump, in order to eliminate contact ofinternal surfaces and moving parts of the pump with irrigant in thefluid supply tube upstream of and towards the wound dressing, and forease of cleaning.

It is of course equally possible to apply a negative pressure to thewound, by means of such a combination of

-   a first device for moving fluid through the wound applied to the    aspirate in the fluid offtake tube downstream of and away from the    wound dressing, and-   a second device for moving fluid through the wound applied to the    irrigant in the fluid supply tube upstream of and towards the wound    dressing; optionally with-   means for supply flow regulation, connected to a fluid supply tube;-   means for aspirate flow regulation, connected to a fluid offtake    tube.

Indeed, as noted below in this regard, preferred embodiments of theapparatus of this first aspect of the present invention for aspirating,irrigating and/or cleansing chronic wounds that apply a negativepressure include such types of combination of

-   a first device, e.g. a diaphragm pump, e.g. preferably a small    portable diaphragm pump, and-   a second device, e.g. a peristaltic pump, preferably a miniature    peristaltic pump,-   as described hereinbefore in relation to the device for moving fluid    through the wound.

As noted above, either of the first device and the second device may bea fixed-throughput device, such as a fixed-speed pump, which willusually require a discrete means for aspirate flow regulation, connectedto a fluid offtake tube, and/or means for supply flow regulation,connected to a fluid supply tube, in each case, e.g. a regulator, suchas a rotary valve, or a variable-throughput device, such as avariable-speed pump, downstream of the wound dressing, thus effectivelyforming a combination of a (first) device for moving fluid through thewound with means for aspirate flow regulation and/or means for supplyflow regulation in a single integral unit.

The higher end of the ranges of % positive and negative pressure notedabove are potentially more suitable for hospital use, where they mayonly be used safely under professional supervision.

The lower end is potentially more suitable for home use, whererelatively high % positive and negative pressures cannot be used safelywithout professional supervision, or for field hospital use.

In each case, the pressure on the wound may be held constant throughoutthe desired length of therapy, or may be varied cyclically in a desiredpositive or negative pressure regime.

As noted above, when it is desired to apply a negative pressure to thewound, it is preferred that the means for providing simultaneousaspiration and irrigation of the wound comprise not only

-   a (first) device for moving fluid through the wound applied to the    aspirate in the fluid offtake tube downstream of and away from the    wound dressing, but also-   a second device for moving fluid through the wound applied to the    irrigant in the fluid supply tube upstream of and towards the wound    dressing.

Accordingly, one embodiment of the apparatus for irrigating, cleansingand/or aspirating wounds of the present invention is characterised inthe means for providing simultaneous aspiration and irrigation of thewound comprises

-   a (first) device for moving fluid through the wound applied to fluid    downstream of and away from the wound dressing, and-   a second device for moving fluid through the wound applied to the    irrigant in the fluid supply tube upstream of and towards the wound    dressing, and in combination with at least one of-   means for supply flow regulation, connected to a fluid supply tube,    and-   means for aspirate flow regulation, connected to a fluid offtake    tube.

As noted above, either of the first device and the second device may bea fixed-throughput device, such as a fixed-speed pump, which willusually require a discrete means for aspirate flow regulation, connectedto a fluid offtake tube, and/or means for supply flow regulation,connected to a fluid supply tube, in each case, e.g. a regulator, suchas a rotary valve, or a variable-throughput device, such as avariable-speed pump, downstream of the wound dressing, thus effectivelyforming a combination of a (first) device for moving fluid through thewound with means for aspirate flow regulation and/or means for supplyflow regulation in a single integral unit.

This combination of

-   a) a device for moving fluid through the wound applied to the    aspirate in the fluid offtake tube downstream of and away from the    wound dressing, and-   b) a device for moving fluid through the wound applied to the fluid    in the fluid supply tube upstream of and towards the wound dressing,-   may be used to apply an overall positive or negative, or even zero    pressure to the wound.

At least one body in the flow path to, over and from the wound bedshould have sufficient resilience against the pressure to allow anysignificant compression or decompression of the fluid occur.

Thus, examples of suitable bodies include those which are or are definedby a film, sheet or membrane, such as inlet or offtake and/or tubes andstructures such as bags, chambers and pouches, filled with irrigantfluid, and e.g. the backing layer of the wound dressing, made ofelastically resilient thermoplastic materials.

It will be seen that the balance of fluid between aspirated fluid fromthe wound and irrigant supplied to the wound from the fluid reservoirwill thus be largely determined by a means for providing simultaneousaspiration and irrigation of the wound which is a system comprising:

-   a) means for aspirate flow regulation and/or a device for moving    fluid through the wound applied to fluid downstream of and away from    the wound dressing, and-   b) means for supply flow regulation and/or a device for moving fluid    through the wound applied to the fluid in the fluid supply tube    upstream of and towards the wound dressing.

As noted above, either of the first device and the second device may bea fixed-throughput device, such as a fixed-speed pump, which willusually require a discrete means for aspirate flow regulation, connectedto a fluid offtake tube, and/or means for supply flow regulation,connected to a fluid supply tube, in each case, e.g. a regulator, suchas a rotary valve, or a variable-throughput device, such as avariable-speed pump, downstream of the wound dressing, thus effectivelyforming a combination of a (first) device for moving fluid through thewound with means for aspirate flow regulation and/or means for supplyflow regulation in a single integral unit.

The same means may be used to apply an overall positive or negative, oreven neutral pressure to the wound.

The appropriate flow rate through the supply tube will depend on anumber of factors, such as

-   the viscosity and consistency of each of the irrigant, exudate and    mixed exudate-irrigant fluid, and any changes as the wound heals;-   the level of negative pressure on the wound bed,-   whether the irrigant in the fluid supply tube upstream of and into    the wound dressing is under positive pressure, and the level of such    pressure;-   the level of any pressure drop between the irrigant in the fluid    supply tube upstream of the wound dressing and the wound bed, such    as across a porous element, e.g. a membrane wound contact layer on    the lower surface of an inlet manifold that delivers the fluid    directly to the wound bed; means for supply flow regulation; and/or    a second device for moving fluid through the wound applied to the    fluid in the fluid supply tube upstream of and towards the wound    dressing;-   the depth and/or capacity of the wound and-   the power consumption needed for a given desired fluid volume flow    rate of irrigant and/or wound exudate through the wound.

The dressing may comprise an inlet manifold (as described in furtherdetail hereinafter) that covers and contacts most of the wound bed withopenings that deliver the fluid directly to the wound bed over anextended area, in the form of one or more inflatable hollow bodiesdefined by a film sheet or membrane.

The (usually small) positive pressure above atmospheric from theirrigation device when both devices are running together should besufficient to inflate the manifold.

The desired fluid volume flow rate of irrigant and/or wound exudate ispreferably that for optimum performance of the wound healing process.

The flow rate will usually be in the range of 1 to 1500 ml/hr, such as 5to 1000 ml/hr, e.g. 15 to 300 ml/hr, such as 35 to 200 ml/hr through thesupply tube. The flow rate through the wound may be held constantthroughout the desired length of therapy, or may be varied cyclically ina desired flow rate regime.

In practice, the offtake rate of flow of total irrigant and/or woundexudate will be of the order of 1 to 2000, e.g. 35 to 300 ml/24 hr/cm²,where the cm² refers to the wound area, depending on whether the woundis in a highly exuding state.

In practice, the rate of exudate flow is only of the order of up to 75microliters/cm²/hr (where cm² refers to the wound area), and the fluidcan be highly mobile or not, depending on the level of proteasespresent). Exudate levels drop and consistency changes as the woundheals, e.g. to a level for the same wound that equates to 12.5-25microliters/cm²/hr.

It will be seen that the aspirated fluid from the wound will typicallycontain a preponderance of irrigant from the fluid reservoir over woundexudate.

The necessary adjustments to maintain the desired balance of fluid bymeans of

-   a) the means for aspirate flow regulation and/or downstream device,    and-   b) the means for supply flow regulation and/or upstream device for    moving fluid will be apparent to the skilled person, bearing in mind    that as noted above, either of the first device and the second    device may be a fixed-throughput device, such as a fixed-speed pump,    which will usually require a discrete means for aspirate flow    regulation, connected to a fluid offtake tube, and/or means for    supply flow regulation, connected to a fluid supply tube, in each    case, e.g. a regulator, such as a rotary valve, or a    variable-throughput device, such as a variable-speed pump,    downstream of the wound dressing, thus effectively forming a    combination of a (first) device for moving fluid through the wound    with means for aspirate flow regulation and/or means for supply flow    regulation in a single integral unit.

The type and/or capacity of

-   a suitable first device for moving fluid through the wound applied    to the aspirate in the fluid offtake tube downstream of and away    from the wound dressing and/or-   a suitable second device for moving fluid through the wound applied    to the irrigant in the fluid supply tube upstream of and towards the    wound dressing and/or-   will be largely determined by-   a) the appropriate or desired fluid volume flow rate of irrigant    and/or wound exudate from the wound, and-   b) whether it is appropriate or desired to apply a positive or    negative pressure to the wound bed, and the level of such pressure    to the wound bed-   for optimum performance of the wound healing process, and by factors    such as portability, power consumption and isolation from    contamination.

As noted above, when it is desired to apply a negative pressure to thewound with the apparatus of this first aspect of the present inventionfor aspirating, irrigating and/or cleansing wounds to providesimultaneous aspiration and irrigation of the wound, the means forproviding simultaneous aspiration and irrigation of the wound maycomprise

-   a single device for moving fluid through the wound applied to the    aspirate in the fluid offtake tube downstream of and away from the    wound dressing or in combination with at least one of-   means for supply flow regulation, connected to a fluid supply tube,    and-   means for aspirate flow regulation, connected to a fluid offtake    tube.

As noted above, the device may be a fixed-throughput device, such as afixed-speed pump, which will usually require a discrete means foraspirate flow regulation, connected to a fluid offtake tube, e.g. aregulator, such as a rotary valve, or a variable-throughput device, suchas a variable-speed pump, downstream of the wound dressing, thuseffectively forming a combination of a device for moving fluid throughthe wound with means for aspirate flow regulation in a single integralunit.

The operation of a typical apparatus of this type for simultaneousaspiration and irrigation of a wound at a low negative pressure of up to20% atm., more usually up to 10% atm. at the wound, with one pump willnow be described.

Before starting the apparatus of this first aspect of the presentinvention for aspirating, irrigating and/or cleansing wounds, thebacking layer of the wound dressing is applied over the wound andconformed to the shape of the bodily part in which the wound is to forma relatively fluid-tight seal or closure.

The means for supply flow regulation, connected to a fluid supply tube,such as a regulator, such as a rotary valve, is usually closed, and themeans for aspirate flow regulation (if any), connected to a fluidofftake tube, is opened.

The aspiration pump is started and run to give a negative pressure of upto 50% atm., more usually up to 20% atm., e.g. up to 10% atm. to beapplied applies a vacuum to the interior of the dressing and the wound.

The means for fluid supply regulation is opened and is then adjusted,and/or where the aspiration pump is a variable-speed pump, downstream ofthe wound dressing, that is adjusted, to maintain the desired balance offluid at a controlled nominal flow rate and to maintain the desirednegative pressure in the interior of the wound dressing.

The apparatus is then run for the desired length of therapy and with thedesired negative pressure regime.

After this period, the aspiration pump is stopped.

The operation of a typical apparatus for simultaneous aspiration andirrigation of a wound at a low negative pressure of up to 20% atm., moreusually up to 10% atm. at the wound, with two pumps will now bedescribed.

The necessary changes where the mode of operation is at a net positivepressure of e.g. up to 15% atm., more usually up to 10% atm. at thewound will be apparent to the skilled person.

Such a typical apparatus for simultaneous aspiration and irrigation of awound at a low negative pressure of up to 20% atm., more usually up to10% atm. at the wound comprises means for providing simultaneousaspiration and irrigation of the wound which is a combination of

-   a) a first device for moving fluid through the wound applied to the    aspirate in the fluid offtake tube downstream of and away from the    wound dressing, with optional means for aspirate flow regulation,    connected to a fluid offtake tube: and-   b) a second device for moving fluid through the wound applied to the    irrigant in the fluid supply tube upstream of and towards the wound    dressing, with optional means for supply flow regulation, connected    to a fluid supply tube.

As noted above, either device may be a fixed-throughput device, such asa fixed-speed pump, which will usually require a discrete means foraspirate flow regulation, connected to a fluid offtake tube, e.g. aregulator, such as a rotary valve, or for irrigant flow regulation,connected to a fluid supply tube, either e.g. a regulator, such as arotary valve, or a variable-throughput device, such as a variable-speedpump, thus effectively forming a combination of a device for movingfluid through the wound with means for flow regulation in a singleintegral unit.

Before starting the apparatus of this first aspect of the presentinvention for aspirating, irrigating and/or cleansing wounds, thebacking layer of the wound dressing is applied over the wound andconformed to the shape of the bodily part in which the wound is to forma relatively fluid-tight seal or closure.

Any means for supply flow regulation, connected to a fluid supply tube,such as a regulator, such as a rotary valve, is usually closed, and anymeans for aspirate flow regulation, connected to a fluid offtake tube,is opened.

The aspiration pump is started and run to apply a negative pressure ofup to 50% atm., more usually up to 20% atm., e.g. up to 10% atm., to theinterior of the dressing and the wound.

The irrigation pump is then started, so that both pumps are runningtogether, and any means for supply flow regulation is opened.

The irrigation pump flow rate and any means for fluid supply regulationare then adjusted and/or where the aspiration pump and/or the irrigationpump is a variable-speed pump, either or both is/are is adjusted, tomaintain the desired balance of fluid at a controlled nominal flow rateand to maintain the desired negative pressure in the interior of thewound dressing.

The apparatus is then run for the desired length of therapy and with thedesired pressure regime.

After this period, the irrigation pump is stopped, shortly followed bythe aspiration pump.

In all embodiments of the apparatus of this first aspect of the presentinvention for aspirating, irrigating and/or cleansing wounds, aparticular advantage is the tendency of the wound dressing to conform tothe shape of the bodily part to which it is applied.

The wound dressing comprises a backing layer with a wound-facing facewhich is capable of forming a relatively fluid-tight seal or closureover a wound and

-   at least one inlet pipe for connection to a fluid supply tube or    tube, which passes through and/or under the wound-facing face, and-   at least one outlet pipe for connection to a fluid offtake tube,    which passes through and/or under the wound-facing face,-   the point at which the or each inlet pipe and the or each outlet    pipe passes through and/or under the wound-facing face forming a    relatively fluid-tight seal or closure.

The term ‘relatively fluid-tight seal or closure’ is used herein toindicate one which is fluid- and microbe-impermeable and permits apositive or negative pressure of up to 50% atm., more usually up to 20%atm., e.g. up to 10% atm. to be applied to the wound. The term ‘fluid’is used herein to include gels, e.g. thick exudate, liquids, e.g. water,and gases, such as air, nitrogen, etc.

The shape of the backing layer that is applied may be any that isappropriate to aspirating, irrigating and/or cleansing the wound acrossthe area of the wound.

Examples of such include a substantially flat film, sheet or membrane,or a bag, chamber, pouch or other structure of the backing layer, e.g.of polymer film, which can contain the fluid.

The backing layer may be a film, sheet or membrane, often with a(generally uniform) thickness of up to 100 micron, preferably up to 50micron, more preferably up to 25 micron, and of 10 micron minimumthickness.

Its largest cross-dimension may be up to 500 mm (for example for largetorso wounds), up to 100 mm (for example for axillary and inguinalwounds), and up to 200 mm for limb wounds (for example for chronicwounds, such as venous leg ulcers and diabetic foot ulcers.

Desirably the dressing is resiliently deformable, since this may resultin increased patient comfort, and lessen the risk of inflammation of awound.

Suitable materials for it include synthetic polymeric materials that donot absorb aqueous fluids, such as polyolefins, such as polyethylenee.g. high-density polyethylene, polypropylene, copolymers thereof, forexample with vinyl acetate and polyvinyl alcohol, and mixtures thereof;polysiloxanes; polyesters, such as polycarbonates; polyamides, e.g. 6-6and 6-10, and hydrophobic polyurethanes.

They may be hydrophilic, and thus also include hydrophilicpolyurethanes.

They also include thermoplastic elastomers and elastomer blends, forexample copolymers, such as ethyl vinyl acetate, optionally or asnecessary blended with high-impact polystyrene.

They further include elastomeric polyurethane, particularly polyurethaneformed by solution casting.

Preferred materials for the present wound dressing include thermoplasticelastomers and curable systems.

The backing layer is capable of forming a relatively fluid-tight seal orclosure over the wound and/or around the inlet and outlet pipe(s).

However, in particular around the periphery of the wound dressing,outside the relatively fluid-tight seal, it is preferably of a materialthat has a high moisture vapour permeability, to prevent maceration ofthe skin around the wound. It may also be a switchable material that hasa higher moisture vapour permeability when in contact with liquids, e.g.water, blood or wound exudate. This may, e.g. be a material that is usedin Smith & Nephew's Allevyn™, IV3000™ and OpSite™ dressings.

The periphery of the wound-facing face of the backing layer may bear anadhesive film, for example, to attach it to the skin around the wound.

This may, e.g. be a pressure-sensitive adhesive, if that is sufficientto hold the wound dressing in place in a fluid-tight seal around theperiphery of the wound-facing face of the wound dressing.

Alternatively or additionally, where appropriate a light switchableadhesive could be used to secure the dressing in place to preventleakage. (A light switchable adhesive is one the adhesion of which isreduced by photocuring. Its use can be beneficial in reducing the traumaof removal of the dressing.)

Thus, the backing layer may have a flange or lip extending around theproximal face of the backing layer, of a transparent or translucentmaterial (for which it will be understood that materials that are listedabove are amongst those that are suitable).

This bears a film of a light switchable adhesive to secure the dressingin place to prevent leakage on its proximal face, and a layer of opaquematerial on its distal face.

To remove the dressing and not cause excessive trauma in removal of thedressing, the layer of opaque material on the distal face of the flangeor lip extending around the proximal wound is removed prior toapplication of radiation of an appropriate wavelength to the flange orlip.

If the periphery of the wound dressing, outside the relativelyfluid-tight seal, that bears an adhesive film to attach it to the skinaround the wound, is of a material that has a high moisture vapourpermeability or is a switchable material, then the adhesive film, ifcontinuous, should also have a high or switchable moisture vapourpermeability, e.g. be an adhesive such as used in Smith & Nephew'sAllevyn™, IV3000™ and OpSite™ dressings.

Where a vacuum is applied to hold the wound dressing in place in afluid-tight seal around the periphery of the wound-facing face of thewound dressing, the wound dressing may be provided with a siliconeflange or lip to seal the dressing around the wound. This removes theneed for adhesives and associated trauma to the patient's skin.

Where the interior of, and the flow of irrigant and/or wound exudate toand through, the dressing is under any significant positive pressure,which will tend to act at peripheral points to lift and remove thedressing off the skin around the wound.

In such use of the apparatus, it may thus be necessary to provide meansfor forming and maintaining such a seal or closure over the woundagainst such positive pressure on the wound, to act at peripheral pointsfor this purpose.

Examples of such means include light switchable adhesives, as above, tosecure the dressing in place to prevent leakage.

Since the adhesion of a light switchable adhesive is reduced byphotocuring, thereby reducing the trauma of removal of the dressing, afilm of a more aggressive adhesive may be used, e.g. on a flange, asabove.

Examples of suitable fluid adhesives for use in more extreme conditionswhere trauma to the patient's skin is tolerable include ones thatconsist essentially of cyanoacrylate and like tissue adhesives, appliedaround the edges of the wound and/or the proximal face of the backinglayer of the wound dressing, e.g. on a flange or lip.

Further suitable examples of such means include adhesive (e.g. withpressure-sensitive adhesive) and non-adhesive, and elastic andnon-elastic straps, bands, loops, strips, ties, bandages, e.g.compression bandages, sheets, covers, sleeves, jackets, sheathes, wraps,stockings and hose, e.g. elastic tubular hose or elastic tubularstockings that are a compressive fit over a limb wound to apply suitablepressure to it when the therapy is applied in this way; and inflatablecuffs, sleeves, jackets, trousers, sheathes, wraps, stockings and hosethat are a compressive fit over a limb wound to apply suitable pressureto it when the therapy is applied in this way.

Such means may each be laid out over the wound dressing to extend beyondthe periphery of the backing layer of the wound dressing, and asappropriate will be adhered or otherwise secured to the skin around thewound and/or itself and as appropriate will apply compression (e.g. withelastic bandages, stockings) to a degree that is sufficient to hold thewound dressing in place in a fluid-tight seal around the periphery ofthe wound,

Such means may each be integral with the other components of thedressing, in particular the backing layer.

Alternatively, it may be permanently attached or releasably attached tothe dressing, in particular the backing layer, with an adhesive film,for example, or these components may be a Velcro™, push snap ortwist-lock fit with each other.

The means and the dressing may be separate structures, permanentlyunattached to each other.

In a more suitable layout for higher positive pressures on the wound, astiff flange or lip extends around the periphery of the proximal face ofthe backing layer of the wound dressing as hereinbefore defined.

The flange or lip is concave on its proximal face to define a peripheralchannel or conduit.

It has a suction outlet that passes through the flange or lip tocommunicate with the channel or conduit and may be connected to a devicefor applying a vacuum, such as a pump or a piped supply of vacuum.

The backing layer may be integral with or attached, for example byheat-sealing, to the flange or lip extending around its proximal face.

To form the relatively fluid-tight seal or closure over a wound that isneeded and to prevent passage of irrigant and/or exudate under theperiphery of the wound-facing face of the wound dressing, in use of theapparatus, the dressing is set on the skin around the wound.

The device then applies a vacuum to the interior of the flange or lip,thus forming and maintaining a seal or closure acting at peripheralpoints around the wound against the positive pressure on the wound.

With all the foregoing means of attachment, and means for forming andmaintaining a seal or closure over the wound, against positive ornegative pressure on the wound at peripheral points around the wound,the wound dressing sealing periphery is preferably of a generally roundshape, such as an ellipse, and in particular circular.

To form the relatively fluid-tight seal or closure over a wound andaround the inlet pipe(s) and outlet pipe(s) at the point at which theypass through and/or under the wound-facing face, the backing layer maybe integral with these other components.

The components may alternatively just be a push, snap or twist-lock fitwith each other, or adhered or heat-sealed together.

The or each inlet pipe or outlet pipe may be in the form of an aperture,such as a funnel, hole, opening, orifice, luer, slot or port forconnection as a female member respectively to a mating end of

-   a fluid tube and/or fluid supply tube (optionally or as necessary    via means for forming a tube, pipe or hose, or nozzle, hole,    opening, orifice, luer, slot or port for connection as a male member    respectively to a mating end of-   a fluid tube and/or fluid supply tube (optionally or as necessary    via means for supply flow regulation) or-   a fluid offtake tube.

Where the components are integral they will usually be made of the samematerial (for which it will be understood that materials that are listedabove are amongst those that are suitable).

Where, alternatively, they are a push, snap or twist-lock fit, the maybe of the same material or of different materials. In either case,materials that are listed above are amongst those that are suitable forall the components.

The or each pipe will generally pass through, rather than under thebacking layer. In such case, the backing layer may often have a rigidand/or resiliently inflexible or stiff area to resist any substantialplay between the or each pipe and the or each mating tube, ordeformation under pressure in any direction.

It may often be stiffened, reinforced or otherwise strengthened by aboss projecting distally (outwardly from the wound) around each relevanttube, pipe or hose, or nozzle, hole, opening, orifice, luer, slot orport for connection to a mating end of a fluid tube and/or fluid supplytube or fluid offtake tube.

Alternatively or additionally, where appropriate the backing layer mayhave a stiff flange or lip extending around the proximal face of thebacking layer to stiffen, reinforce or otherwise strengthen the backinglayer.

The wound dressing may not comprise any integer under the backing layerin the wound in use.

However, this may not provide a system to distribute irrigant over asufficient functional surface area to irrigate the wound at a practicalrate to be suitable for use, in particular in chronic wound aspirationand irrigation, with relatively high concentrations of materials thatare deleterious to wound healing.

It may be advantageous to provide a system where wound irrigant may bedistributed more evenly, or pass in a more convoluted path under thedressing over the wound bed.

Accordingly, one form of the dressing is provided with a ‘tree’ form ofpipes, tubes or tubules that radiate from an inlet manifold to the woundbed to end in apertures and deliver the aspirating fluid directly to thewound bed via the apertures. Similarly, there is an outlet manifold fromwhich tubules radiate and run to the wound bed to end in openings andcollect the fluid directly from the wound bed.

The pipes, etc. may radiate regularly or irregularly through the woundin use, respectively from the inlet or outlet manifold, althoughregularly may be preferred. A more suitable layout for deeper wounds isone in which the pipes, etc. radiate hemispherically and concentrically,to the wound bed.

For shallower wounds, examples of suitable forms of such layout of thepipes, etc. include ones in which the pipes, etc. radiate in a flattenedhemiellipsoid and concentrically, to the wound bed.

Other suitable forms of layout of the pipes, etc. include one which havepipes, tubes or tubules extending from the inlet pipe(s) and/or outletpipe(s) at the point at which they pass through and/or under thewound-facing face of the backing layer to run over the wound bed. Thesemay have a blind bore with perforations, apertures, holes, openings,orifices, slits or slots along the pipes, etc.

These pipes, etc. then effectively form an inlet pipe manifold thatdelivers the aspirating fluid directly to the wound bed or outlet pipeor collects the fluid directly from the wound respectively.

It does so via the holes, openings, orifices, slits or slots in thetubes, pipes, tubules, etc. over most of the wound bed under the backinglayer.

It may be desirable that the tubes, pipes or tubules are resilientlyflexible, e.g. elastomeric, and preferably soft, structures with goodconformability in the wound and the interior of the wound dressing.

When the therapy is applied in this way, the layout of the tubes, pipes,tubules, etc. may depend on the depth and/or capacity of the wound.

Thus, for shallower wounds, examples of suitable forms of such layout ofthe tubes, pipes, tubules, etc. include ones that consist essentially ofone or more of the tubes, etc in a spiral.

A more suitable layout for deeper wounds when the therapy is applied inthis way may be one which comprises one or more of the tubes, etc in ahelix or spiral helix.

Other suitable layouts for shallower wounds include one which haveblind-bore, perforated inlet pipe or outlet pipe manifolds that aspiratefluid in the wound when the dressing is in use.

One or both of these may be such a form, the other may be, e.g. one ormore straight blind-bore, perforated radial tubes, pipes or nozzles.

A preferred form of inlet pipe (or less usually) outlet pipe manifoldthat delivers the aspirating fluid directly to the wound bed or collectsthe fluid directly from the wound respectively is one that comprise oneor more conformable hollow bodies defined by a film, sheet or membrane,such as a bag, chamber, pouch or other structure, filled with theirrigant (or less usually) aspirate from the wound, passing throughperforations, apertures, holes, openings, orifices, slits or slots inthe film, sheet or membrane defining the hollow body or hollow bodies.

These may be of small cross-dimension, so that they may then effectivelyform microperforations, microapertures or pores in a permeable integer,for example the polymer film, sheet or membrane.

This type of manifold for irrigation (more usually) provides the highestuniformity in the flow distribution of irrigant over the wound at apractical rate to be suitable for use, in particular in chronic woundaspiration and irrigation, and hence to provide a system where materialsthat are beneficial in promoting wound healing, such as growth factors,cell matrix components, and other physiologically active components ofthe exudate from a wound, are distributed more evenly under the dressingover the wound bed.

This type of manifold for irrigation (more usually) is noted below withregard to wound fillers under the backing layer, since it is aresiliently flexible, e.g. elastomeric, and soft, structure with goodconformability to wound shape. It is urged by its own resilience againstthe backing layer to apply gentle pressure on the wound bed, and istherefore also capable of acting as a wound filler. The film, sheet ormembrane, often has a (generally uniform) thickness similar to that offilms or sheets used in conventional wound dressing backing layers.

Another suitable layout is one in which

-   an inlet pipe and/or outlet pipe manifold that delivers the    aspirating fluid directly to the wound bed or collects the fluid    directly from the wound respectively-   via inlet and/or outlet tubes, pipes or tubules,-   and the inlet manifold and/or outlet manifold is formed by slots in    layers permanently attached to each other in a stack, and-   the inlet and/or outlet tubes, pipes or tubules are formed by    apertures through layers permanently attached to each other in a    stack. (In FIG. 10 a there is shown an exploded isometric view of    such a stack, which is non-limiting.)

As also mentioned herein, the backing layer that is applied may be anythat is appropriate to the present system of therapy and permits apositive or negative pressure of up to 50% atm., more usually up to 25%atm. to be applied to the wound.

It is thus often a microbe-impermeable film, sheet or membrane, which issubstantially flat, depending on any pressure differential on it, andoften with a (generally uniform) thickness similar to such films orsheets used in conventional wound dressings, i.e. up to 100 micron,preferably up to 50 micron, more preferably up to 25 micron, and of 10micron minimum thickness.

The backing layer may often have a rigid and/or resiliently inflexibleor stiff area to resist any substantial play between other componentsthat are not mutually integral, and may be stiffened, reinforced orotherwise strengthened, e.g. by a projecting boss.

Such a form of dressing would not be very conformable to the wound bed,and may effectively form a chamber, hollow or cavity defined by abacking layer and the wound bed under the backing layer.

It may be desirable that the interior of the wound dressing conform tothe wound bed, even for a wound in a highly exuding state. Accordingly,one form of the dressing is provided with a wound filler under thebacking layer.

This is favourably a resiliently flexible, e.g. elastomeric, andpreferably soft, structure with good conformability to wound shape.

It is urged by its own resilience against the backing layer to applygentle pressure on the wound bed.

The wound filler may be integral with the other components of thedressing, in particular the backing layer.

Alternatively, it may be permanently attached to them/it, with anadhesive film, for example, or by heat-sealing, e.g. to a flange or lipextending from the proximal face, so a not to disrupt the relativelyfluid-tight seal or closure over the wound that is needed.

Less usually, the wound filler is releasably attached to the backinglayer, with an adhesive film, for example, or these components may be apush, snap or twist-lock fit with each other.

The wound filler and the backing layer may be separate structures,permanently unattached to each other.

The wound filler may be or comprise a solid integer, favourably aresiliently flexible, e.g. elastomeric, and preferably soft, structurewith good conformability to wound shape.

Examples of suitable forms of such wound fillers are foams formed of asuitable material, e.g. a resilient thermoplastic.

Preferred materials for the present wound dressing include reticulatedfiltration polyurethane foams with small apertures or pores.

Alternatively or additionally, it may be in the form of, or comprise oneor more conformable hollow bodies defined by a film, sheet or membrane,such as a bag, chamber, pouch or other structure, filled with a fluid orsolid that urges it to the wound shape.

The film, sheet or membrane, often has a (generally uniform) thicknesssimilar to that of films or sheets used in conventional wound dressingbacking layers.

That is, up to 100 micron, preferably up to 50 micron, more preferablyup to 25 micron, and of 10 micron minimum thickness, and is oftenresiliently flexible, e.g. elastomeric, and preferably soft.

Such a filler is often integral with the other components of thedressing, in particular the backing layer, or permanently attached tothem/it, with an adhesive film, for example, or by heat-sealing, e.g. toa flange

Examples of suitable fluids contained in the hollow body or bodiesdefined by a film, sheet or membrane include gases, such as air,nitrogen and argon, more usually air, at a small positive pressure aboveatmospheric; and liquids, such as water, saline.

Examples also include gels, such as silicone gels, e.g. CaviCare™ gel,or preferably cellulosic gels, for example hydrophilic cross-linkedcellulosic gels, such as Intrasite™ cross-linked materials.

Examples also include aerosol foams, where the gaseous phase of theaerosol system is air or an inert gas, such as nitrogen or argon, moreusually air, at a small positive pressure above atmospheric; and solidparticulates, such as plastics crumbs.

Of course, if the backing layer is a sufficiently conformable and/ore.g. an upwardly dished sheet, the backing layer may lie under the woundfiller, rather than vice versa.

In this type of layout, in order for the wound filler to urge the wounddressing towards the wound bed, it will usually have to be firmlyadhered or otherwise releasably attached to the skin around the wound.This is especially the case in those embodiments where the wound fillerand the backing layer are separate structures, permanently unattached toeach other.

In such a layout for deeper wounds when the therapy is applied in thisway, the means for such attachment may also form and maintain a seal orclosure over the wound.

Where the filler is over the backing layer, and the fluid inlet pipe(s)and outlet pipe(s) pass through the wound-facing face of the backinglayer, they may run through or around the wound filler over the backinglayer.

One form of the dressing is provided with a wound filler under thebacking layer that is or comprises a resiliently flexible, e.g.elastomeric, and preferably soft, hollow body defined by a film, sheetor membrane, such as a bag, chamber, pouch or other structure.

It has apertures, holes, openings, orifices, slits or slots, or tubes,pipes, tubules or nozzles. It communicates with at least one inlet oroutlet pipe through at least one aperture, hole, opening, orifice, slitor slot.

The fluid contained in the hollow body may then be the aspirating fluidin the apparatus.

The hollow body or each of the hollow bodies then effectively forms aninlet pipe or outlet pipe manifold that delivers the aspirating fluiddirectly to the wound bed or collects the fluid directly from the woundrespectively via the holes, openings, orifices, slits or slots, or thetubes, pipes or hoses, etc. in the film, sheet or membrane.

When the therapy is applied in this way, the type of the filler may alsobe largely determined by the depth and/or capacity of the wound.

Thus, for shallower wounds, examples of suitable wound fillers as acomponent of a wound dressing include ones that consist essentially ofone or more conformable hollow bodies defining an inlet pipe and/oroutlet pipe manifold that delivers the aspirating fluid directly to thewound bed or collects the fluid directly from the wound.

A more suitable wound filler for deeper wounds when the therapy isapplied in this way may be one which comprises one or more conformablehollow bodies defined by, for example a polymer film, sheet or membrane,that at least partly surround(s) a solid integer. This may provide asystem with better rigidity for convenient handling.

The wound filler under the backing layer may effectively form an inletpipe or outlet pipe manifold,

If not, in order for aspiration and/or irrigation of the wound bed tooccur, it is appropriate for one or more bores, channels, conduits,passages, pipes, tubes, tubules and/or spaces, etc. to run from thepoint at which the fluid inlet pipe(s) and outlet pipe(s) pass throughand/or under the wound-facing face of the backing layer through oraround the wound filler under the backing layer.

Less usually, the wound filler is an open-cell foam with pores that mayform such bores, channels, conduits, passages and/or spaces through thewound filler under the backing layer.

Where the filler is or comprises one or more conformable hollow bodiesdefined by, for example a polymer film, sheet or membrane, it may beprovided with means for admitting fluids to the wound bed under thewound dressing.

These may be in the form of pipes, tubes, tubules or nozzles runningfrom the point at which the fluid inlet pipe(s) and outlet pipe(s) passthrough and/or under the wound-facing face of the backing layer throughor around the wound filler under the backing layer.

All of the suitable layouts for shallower wounds that compriseblind-bore, perforated inlet pipe or outlet pipe manifolds that aspiratefluid in the wound when the dressing is in use, that are describedhereinbefore, may be used under a wound filler under the backing layer.

In brief, suitable layouts include ones where one or both manifolds areannular or toroidal (regular, e.g. elliptical or circular or irregular),optionally with blind-bore, perforated radial tubes, pipes or nozzles,branching from the annulus or torus; and/or

-   in a meandering, tortuous, winding, zigzag, serpentine or    boustrophedic (i.e. in the manner of a ploughed furrow) pattern, or-   defined by slots in and apertures through layers attached to each    other in a stack.

The inlet and/or outlet tubes, the fluid tube and the fluid supply tube,etc. may be of conventional type, e.g. of elliptical or circularcross-section, and may suitably have a uniform cylindrical bore,channel, conduit or passage throughout their length, and suitably thelargest cross-dimension of the bore may be up to 10 mm for large torsowounds, and up to 2 mm for limb wounds.

The tube walls should suitably thick enough to withstand any positive ornegative pressure on them. However, the prime purpose of such tubes isto convey fluid irrigant and exudate through the length of the apparatusflow path, rather than to act as pressure vessels.

The tube walls may suitably be at least 25 micron thick.

The bore or any perforations, apertures, holes, openings, orifices,slits or slots along the pipes, etc. or in the hollow body or each ofthe hollow bodies may be of small cross-dimension.

They may then effectively form a macroscopic and/or microscopic filterfor particulates including cell debris and micro-organisms, whilstallowing proteins and nutrients to pass through.

Such tubes, pipes or hoses, etc. through and/or around the filler,whether the latter is a solid integer and/or one or more resilientlyflexible or conformable hollow bodies, are described in further detailhereinbefore in connection with the inlet pipe(s) and outlet pipe(s).

The whole length of the apparatus for aspirating, irrigating and/orcleansing wounds should be microbe-impermeable once the wound dressingis over the wound in use.

It is desirable that the wound dressing and the interior of theapparatus for aspirating, irrigating and/or cleansing wounds of thepresent invention is sterile.

The fluid may be sterilised in the fluid reservoir and/or the rest ofthe system in which the fluid moves by ultraviolet, gamma or electronbeam irradiation.

This way, in particular reduces or eliminates contact of internalsurfaces and the fluid with any sterilising agent.

Examples of other methods of sterilisation of the fluid also includee.g. the use of

-   ultrafiltration through microapertures or micropores, e.g. of 0.22    to 0.45 micron maximum cross-dimension, to be selectively    impermeable to microbes; and-   fluid antiseptics, such as solutions of chemicals, such as    chlorhexidine and povidone iodine; metal ion sources, such as silver    salts, e.g. silver nitrate; and hydrogen peroxide;-   although the latter involve contact of internal surfaces and the    fluid with the sterilising agent.

It may be desirable that the interior of the wound dressing, the rest ofthe system in which the fluid moves, and/or the wound bed, even for awound in a highly exuding state, are kept sterile after the fluid issterilised in the fluid reservoir, or that at least naturally occurringmicrobial growth is inhibited.

Thus, materials that are potentially or actually beneficial in thisrespect may be added to the irrigant initially, and as desired theamount in increased by continuing addition.

Examples of such materials include antibacterial agents (some of whichare listed above), and antifungal agents.

Amongst those that are suitable are, for example triclosan, iodine,metronidazole, cetrimide, chlorhexidine acetate, sodium undecylenate,chlorhexidine and iodine.

Buffering agents, such as potassium dihydrogen phosphate/disodiumhydrogen phosphate. may be added to adjust the pH, as may localanalgesics/anaesthetics, such as lidocaine lignocaine/lignocainehydrochloride, xylocalne (adrenaline, lidocaine) and/oranti-inflammatories, to reduce wound pain or inflammation or painassociated with the dressing.

In order to combat the deposition of materials in the flow path from theirrigant, a repellent coating may be used at any point or on any integerin the path in direct contact with the fluid, e.g. on the means forproviding simultaneous aspiration and irrigation of the wound or anydesired tube or pipe.

Examples of coating materials for surfaces over which the aspiratingfluid passes include

-   anticoagulants, such as heparin, and-   high surface tension materials, such as PTFE, and polyamides,-   which are useful for growth factors, enzymes and other proteins and    derivatives.

The apparatus of the invention for aspirating, irrigating and/orcleansing wounds is provided with means for admitting fluids directly orindirectly to the wound under the wound dressing in the form of a fluidsupply tube to a fluid reservoir.

The fluid reservoir may be of any conventional type, e.g. a tube, bag(such as a bag typically used for blood or blood products, e.g. plasma,or for infusion feeds, e.g. of nutrients), chamber, pouch or otherstructure, e.g. of polymer film, which can contain the irrigant fluid.

The reservoir may be made of a film, sheet or membrane, often with a(generally uniform) thickness similar to that of films or sheets used inconventional wound dressing backing layers, i.e. up to 100 micron,preferably up to 50 micron, more preferably up to 25 micron, and of 10micron minimum thickness, and is often a resiliently flexible, e.g.elastomeric, and preferably soft, hollow body.

In all embodiments of the apparatus the type and material of the tubesthroughout the apparatus of the invention for aspirating, irrigatingand/or cleansing wounds and the fluid reservoir will be largelydetermined by their function.

To be suitable for use, in particular on chronic timescales, thematerial should be non-toxic and biocompatible, inert to any activecomponents, as appropriate of the irrigant from the fluid reservoirand/or wound exudate in the apparatus flow path, and, in any use of atwo-phase system aspiration and irrigation unit, of the dialysate thatmoves into the aspirating fluid in the apparatus.

When in contact with irrigant fluid, it should not allow any significantamounts of extractables to diffuse freely out of it in use of theapparatus.

It should be sterilisable by ultraviolet, gamma or electron beamirradiation and/or with fluid antiseptics, such as solutions ofchemicals, fluid- and microbe-impermeable once in use, and flexible.

Examples of suitable materials for the fluid reservoir include syntheticpolymeric materials, such as polyolefins, such as polyethylene,high-density polyethylene and polypropylene.

Suitable materials for the present purpose also include copolymersthereof, for example with vinyl acetate and mixtures thereof. Suitablematerials for the present purpose further include medical gradepoly(vinyl chloride).

Notwithstanding such polymeric materials, the fluid reservoir will oftenhave a stiff area to resist any substantial play between it andcomponents that are not mutually integral, such as the fluid supply tubetowards the wound dressing, and may be stiffened, reinforced orotherwise strengthened, e.g. by a projecting boss.

Materials deleterious to wound healing that are removed include

oxidants, such as free radicals, e.g. peroxide and superoxide;

-   iron II and iron III;-   all involved in oxidative stress on the wound bed;-   proteases, such as serine proteases, e.g. elastase and thrombin;    cysteine proteases; matrix metalloproteases, e.g. collagenase; and    carboxyl (acid) proteases;-   endotoxins, such as lipopolysaccharides;-   autoinducer signalling molecules, such as homoserine lactone    derivatives, e.g. oxo-alkyl derivatives;-   inhibitors of angiogenesis such as thrombospondin-1 (TSP-1),    plasminogen activator inhibitor, or angiostatin (plasminogen    fragment);-   pro-inflammatory cytokines such as tumour necrosis factor alpha    (TNFα) and interleukin 1 beta (IL-1β),-   oxidants, such as free radicals, e.g., e.g. peroxide and superoxide;    and metal ions, e.g. iron II and iron III, all involved in oxidative    stress on the wound bed.

It is believed that aspirating wound fluid aids in removal from of thematerials deleterious to wound healing from wound exudate and/orirrigant, whilst distributing materials that are beneficial in promotingwound healing in contact with the wound.

A steady state concentration equilibrium of materials beneficial inpromoting wound healing may be set up between in the irrigant and/orwound exudate.

Aspirating wound fluid aids in the quicker attainment of thisequilibrium

Materials beneficial to wound healing that are distributed includecytokines, enzymes, growth factors, cell matrix components, biologicalsignalling molecules and other physiologically active components of theexudate and/or

-   materials in the irrigant that are potentially or actually    beneficial in respect of wound healing, such as nutrients for wound    cells to aid proliferation, gases, such as oxygen.

The conduits through which respectively the irrigant and/or woundexudate passes to and from the wound dressing and

-   i) may have means for modular disconnection and withdrawal of the    dressing,-   ii) providing an immediate fluid-tight seal or closure over the ends    of the conduits and the cooperating tubes in the rest of the    apparatus of the invention so exposed,-   to prevent continuing passage of irrigant and/or exudate.

The outlet from the means for aspirate flow regulation and/or tubes maybe collected and monitored and used to diagnose the status of the woundand/or its exudate.

Any aspirate collection vessel may be of any conventional type, e.g. atube, bag (such as a bag typically used as an ostomy bag), chamber,pouch or other structure, e.g. of polymer film, which can contain theirrigant fluid that has been bled off. In all embodiments of theapparatus, the type and material of the aspirate collection vessel willbe largely determined by its function.

To be suitable for use, the material need only be fluid-impermeable oncein use, and flexible.

Examples of suitable materials for the fluid reservoir include syntheticpolymeric materials, such as polyolefins, such as poly(vinylidenechloride).

Suitable materials for the present purpose also include polyethylene,e.g. high-density polyethylene, polypropylene, copolymers thereof, forexample with vinyl acetate and mixtures thereof.

In a second aspect of the present invention there is provided aconformable wound dressing, characterised in that it comprises a backinglayer with a wound-facing face which is capable of forming a relativelyfluid-tight seal or closure over a wound and has

-   at least one inlet pipe for connection to a fluid supply tube, which    passes through and/or under the wound-facing face, and-   at least one outlet pipe for connection to a fluid offtake tube,    which passes through and/or under the wound-facing face,-   the point at which the or each inlet pipe and the or each outlet    pipe passes through and/or under the wound-facing face forming a    relatively fluid-tight seal or closure over the wound.

The dressing is advantageously provided for use in a bacteria-proofpouch.

Examples of suitable forms of such wound dressings are as described byway of example hereinbefore.

In a third aspect of the present invention there is provided a method oftreating wounds to promote wound healing using the apparatus foraspirating, irrigating and/or cleansing wounds of the present invention.

The present invention will now be described by way of example only withreference to the accompanying drawings in which:

FIG. 1 is a schematic view of an apparatus for aspirating, irrigatingand/or cleansing a wound according to the first aspect of the presentinvention that has

-   a single device for moving fluid through the wound applied to the    aspirate in the fluid offtake tube downstream of and away from the    wound dressing, in combination with-   means for supply flow regulation, connected to a fluid supply tube,    and means for aspirate flow regulation, connected to a fluid offtake    tube.

FIG. 2 is a schematic view of another apparatus for aspirating,irrigating and/or cleansing a wound according to the first aspect of thepresent invention that has

-   a first device for moving fluid through the wound applied to the    aspirate in the fluid offtake tube downstream of and away from the    wound dressing, with means for aspirate flow regulation, connected    to a fluid offtake tube; and-   a second device for moving fluid through the wound applied to the    irrigant in the fluid supply tube upstream of and towards the wound    dressing.

FIGS. 3 to 7 are cross-sectional views of conformable wound dressings,of the second aspect of the present invention for aspirating and/orirrigating wounds.

In these, FIGS. 3 a to 6 a are cross-sectional plan views of the wounddressings, and FIGS. 3 b to 6 b are cross-sectional side views of thewound dressings.

FIGS. 8 to 10 are various views of inlet and outlet manifold layouts forthe wound dressings of the second aspect of the present invention forrespectively delivering fluid to, and collecting fluid from, the wound.

FIGS. 11A to D are variants of a two-pump system with essentiallyidentical, and identically numbered, components as in FIG. 2, exceptthat there is

-   a pump bypass loop, except in FIG. 11C.-   a filter downstream of the aspirate collection vessel, and-   a bleed regulator, such as a rotary valve, connected to the fluid    offtake tube or to the wound space, for the regulation of the    positive or negative pressure applied to the wound.

FIGS. 12A to C are variants of a two-pump system with essentiallyidentical, and identically numbered, components as in FIG. 11, exceptthat they have various means for varying the regulation of the positiveor negative pressure applied to the wound.

FIGS. 13 to 26 are cross-sectional views of conformable wound dressings,of the second aspect of the present invention for aspirating and/orirrigating wounds.

FIG. 27 a is a plan view and FIG. 27 b a cross-sectional view of afurther conformable wound dressings of the second aspect of the presentinvention for aspirating and/or irrigating wounds.

FIGS. 28A and B are variants of a two-pump system with essentiallyidentical, and identically numbered, components as in FIG. 11.

However, they have alternative means for handling the aspirate flow tothe aspirate collection vessel under negative or positive pressure tothe wound in simultaneous aspiration and irrigation of the wound,including in FIG. 27B a third device for moving fluid into a waste bag.

FIG. 29 is a single-pump system essentially with the omission from theapparatus of FIG. 11 of the second device for moving irrigant fluid intothe wound dressing.

FIG. 30 is an apparatus where an irrigant is delivered continually tothe wound bed and the resultant wound exudate/fluid mixture is at thesame time continually aspirated from the wound.

Referring to FIG. 1, the apparatus (1) for aspirating, irrigating and/orcleansing wounds comprises

-   a conformable wound dressing (2), having-   a backing layer (3) which is capable of forming a relatively    fluid-tight seal or closure (4) over a wound (5) and-   one inlet pipe (6) for connection to a fluid supply tube (7), which    passes through the wound-facing face of the backing layer (5) at    (8), and-   one outlet pipe (9) for connection to a fluid offtake tube (10),    which passes through the wound-facing face at (11),-   the points (8), (11) at which the inlet pipe and the outlet pipe    passes through and/or under the wound-facing face forming a    relatively fluid-tight seal or closure over the wound;-   the inlet pipe being connected via means for supply flow regulation,    here a valve (14), by the fluid supply tube (7) to a fluid reservoir    (12), and-   the outlet pipe (9) being connected via means for aspirate flow    regulation, here a valve (16) and a fluid offtake tube (10) to    waste, e.g. to a collection bag (not shown);-   a device for moving fluid through the wound (17), here a diaphragm    pump (18), e.g. preferably a small portable diaphragm pump, acting    on the fluid aspiration tube (13) to apply a low negative pressure    on the wound; and-   the valve (14) in the fluid supply tube (7), the valve (16) in the    fluid offtake tube (10), and the diaphragm pump (18), providing    means for providing simultaneous aspiration and irrigation of the    wound (5),-   such that fluid may be supplied to fill the flowpath from the fluid    reservoir via the fluid supply tube (via the means for supply flow    regulation) and moved by the device through the flow path.

The operation of the apparatus is as described hereinbefore.

Referring to FIG. 2, the apparatus (21) is a variant two-pump systemwith essentially identical, and identically numbered, components as inFIG. 1, except that

-   there is no means for supply flow regulation in the fluid supply    tube (7) from the fluid reservoir (12), and-   there is-   a first device for moving fluid through the wound (5), here a    diaphragm pump (18A), e.g. preferably a small portable diaphragm    pump, acting on the fluid aspiration tube (13) downstream of and    away from the wound dressing to apply a low negative pressure on the    wound; with-   means for negative pressure regulation, here a valve (16) connected    to the vacuum tube (13) and a vacuum vessel (aspirate collection    jar) (19); and-   a second device for moving fluid through the wound (5), here a    peristaltic pump (18B), e.g. preferably a small portable diaphragm    pump, applied to the irrigant in the fluid supply tube (7) upstream    of and towards the wound dressing,-   the first device (18A) and second device (18B), and the valve (16)    in the vacuum tube (13), and the diaphragm pump (18), providing    means for providing simultaneous aspiration and irrigation of the    wound (5), such that fluid may be supplied to fill the flowpath from    the fluid reservoir via the fluid supply tube (via the means for    supply flow regulation) and moved by the devices through the flow    path.

The operation of the apparatus is as described hereinbefore

Referring to FIGS. 3 to 6, each dressing (41) is in the form of aconformable body defined by a microbe-impermeable film backing layer(72) with a uniform thickness of 25 micron.

It has a wound-facing face (43), which is capable of forming arelatively fluid-tight seal or closure over a wound.

The backing layer (72) extends in use on a wound over the skin aroundthe wound.

On the proximal face of the backing layer (43) on the overlap (44), itbears an adhesive film (45), to attach it to the skin sufficiently tohold the wound dressing in place in a fluid-tight seal around theperiphery of the wound-facing face (43) of the wound dressing.

There is one inlet pipe (76) for connection to a fluid supply tube (notshown), which passes through and/or under the wound-facing face (43),and one outlet pipe (77) for connection to a fluid offtake tube (notshown), which passes through and/or under the wound-facing face (43),

Referring to FIGS. 3 a and 3 b, one form of the dressing is providedwith a wound filler (48) under a circular backing layer (42).

This comprises a generally frustroconical, toroidal conformable hollowbody, defined by a membrane (49) which is filled with a fluid, here airor nitrogen, that urges it to the wound shape.

The filler (48) may be permanently attached to the backing layer with anadhesive film (not shown) or by heat-sealing.

The inlet pipe (46) and outlet pipe (47) are mounted centrally in thebacking layer (42) above the central tunnel (50) of the toroidal hollowbody (48) and each passes through the backing layer (42).

Each extends in pipes (51) and (52) respectively through the tunnel (50)of the toroidal hollow body (48) and then radially in diametricallyopposite directions under the body (48).

This form of the dressing is a more suitable layout for deeper wounds.

Referring to FIGS. 4 a and 4 b, a more suitable form for shallowerwounds is shown.

This comprises a circular backing layer (42) and a circular upwardlydished first membrane (61) with apertures (62) that is permanentlyattached to the backing layer (42) by heat-sealing to form a circularpouch (63).

The pouch (63) communicates with the inlet pipe (46) through a hole(64), and thus effectively forms an inlet pipe manifold that deliversthe aspirating fluid directly to the wound when the dressing is in use.

An annular second membrane (65) with openings (66) is permanentlyattached to the backing layer (42) by heat-sealing to form an annularchamber (67) with the layer (42).

The chamber (67) communicates with the outlet pipe (47) through anorifice (68), and thus effectively forms an outlet pipe manifold thatcollects the fluid directly from the wound when the dressing is in use.

Referring to FIGS. 5 a and 5 b, a variant of the dressing of FIGS. 4 aand 4 b that is a more suitable form for deeper wounds is shown.

This comprises a circular backing layer (42) and a filler (69), in theform of an inverted frustroconical, solid integer, here a resilientelastomeric foam, formed of a thermoplastic, or preferably across-linked plastics foam.

It may be permanently attached to the backing layer (42), with anadhesive film (not shown) or by heat-sealing.

A circular upwardly dished sheet (70) lies under and conforms to, but isa separate structure, permanently unattached to, the backing layer (42)and the solid integer (69).

A circular upwardly dished first membrane (71) with apertures (72) ispermanently attached to the sheet (70) by heat-sealing to form acircular pouch (73) with the sheet (70).

The pouch (73) communicates with the inlet pipe (46) through a hole(74), and thus effectively forms an inlet pipe manifold that deliversthe aspirating fluid directly to the wound when the dressing is in use.

An annular second membrane (75) with openings (76) is permanentlyattached to the sheet (70) by heat-sealing to form an annular chamber(77) with the sheet (70).

The chamber (77) communicates with the outlet pipe (47) through anorifice (78), and thus effectively forms an outlet pipe manifold thatcollects the fluid directly from the wound when the dressing is in use.

Alternatively, where appropriate the dressing may be provided in a formin which the circular upwardly dished sheet (70) functions as thebacking layer and the solid filler (69) sits on the sheet (70) as thebacking layer, rather than under it. The filler (69) is held in placewith an adhesive film or tape, instead of the backing layer (42).

Referring to FIGS. 6 a and 6 b, a dressing that is a more suitable formfor deeper wounds is shown.

This comprises a circular backing layer (42) and a filler (79), in theform of an inverted generally hemispherical integer, permanentlyattached to the backing layer with an adhesive film (not shown) or byheat-sealing. Here it is a resilient elastomeric foam or a hollow bodyfilled with a fluid, here a gel that urges it to the wound shape.

The inlet pipe (46) and outlet pipe (47) are mounted peripherally in thebacking layer (42).

A circular upwardly dished sheet (80) lies under and conforms to, but isa separate structure, permanently unattached to, the backing layer (42)and the filler (79).

A circular upwardly dished bilaminate membrane (81) has a closed channel(82) between its laminar components, with

-   perforations (83) along its length on the outer surface (84) of the    dish formed by the membrane (81) and-   an opening (85) at the outer end of its spiral helix, through which    the channel (82) communicates with the inlet pipe (46),-   and thus effectively forms an inlet pipe manifold that delivers the    aspirating fluid directly to the wound when the dressing is in use.

The membrane (81) also has apertures (86) between and along the lengthof the turns of the channel (82).

The inner surface (87) of the dish formed by the membrane (81) ispermanently attached at its innermost points (88) with an adhesive film(not shown) or by heat-sealing to the sheet (80). This defines a matingclosed spirohelical conduit (89).

At the outermost end of its spiral helix, the conduit (89) communicatesthrough an opening (90) with the outlet pipe (47) and is thuseffectively an outlet manifold to collect the fluid directly from thewound via the apertures (86).

Referring to FIGS. 7 a and 7 b, one form of the dressing is providedwith a circular backing layer (42).

A first (larger) inverted hemispherical membrane (92) is permanentlyattached centrally to the layer (42) by heat-sealing to form ahemispherical chamber (94) with the layer (42).

A second (smaller) concentric hemispherical membrane (93) within thefirst is permanently attached to the layer (42) by heat-sealing to forma hemispherical pouch (95).

The pouch (95) communicates with the inlet pipe (46) and is thuseffectively an inlet manifold, from which pipes (97) radiatehemispherically and run to the wound bed to end in apertures (98). Thepipes (97) deliver the aspirating fluid directly to the wound bed viathe apertures (98).

The chamber (94) communicates with the outlet pipe (47) and is thuseffectively an outlet manifold from which tubules (99) radiatehemispherically and run to the wound bed to end in openings (100). Thetubules (99) collect the fluid directly from the wound via the openings(100).

Referring to FIGS. 8 a to 8 d, one form of the dressing is provided witha square backing layer (42) and

-   first tube (101) extending from the inlet pipe (46), and-   second tube (102) extending from the outlet pipe (47)-   at the points at which they pass through the backing layer, to run    over the wound bed.

These pipes (101), (102) have a blind bore with orifices (103), (104)along the pipes (101), (102).

These pipes (101), (102) respectively form an inlet pipe or outlet pipemanifold that delivers the aspirating fluid directly to the wound bed orcollects the fluid directly from the wound respectively via theorifices.

In FIGS. 8 a and 8 d, one layout of each of the pipes (101), (102) asinlet pipe and outlet pipe manifolds is a spiral.

In FIG. 8 b, the layout is a variant of that of FIGS. 8 a and 8 b, withthe layout of the inlet manifold (101) being a full or partial torus,and the outlet manifold (102) being a radial pipe.

Referring to FIG. 8 c, there is shown another suitable layout in whichthe inlet manifold (101) and the outlet manifold (102) run alongsideeach other over the wound bed in a boustrophedic pattern, i.e. in themanner of ploughed furrows.

Referring to FIGS. 9 a to 9 d, there are shown other suitable layoutsfor deeper wounds, which are the same as shown in FIGS. 8 a to 8 d. Thesquare backing layer (42) however has a wound filler (110) under, andmay be permanently attached to, the backing layer (42), with an adhesivefilm (not shown) or by heat-sealing, which is an inverted hemisphericalsolid integer, here a resilient elastomeric foam, formed of athermoplastic, preferably a cross-linked plastics foam.

Under the latter is a circular upwardly dished sheet (111) whichconforms to, but is a separate structure, permanently unattached to, thesolid filler (110). Through the sheet (111) pass the inlet pipe (46) andthe outlet pipe (47), to run over the wound bed. These pipes (101),(102) again have a blind bore with orifices (103), (104) along the pipes(101), (102).

Alternatively (as in FIGS. 5 a and 5 b), where appropriate the dressingmay be provided in a form in which the circular upwardly dished sheet(111) functions as the backing layer and the solid filler (110) sits onthe sheet (42) as the backing layer, rather than under it. The filler(110) is held in place with an adhesive film or tape, instead of thebacking layer (42).

In FIGS. 10 a to 10 c, inlet and outlet manifolds for the wounddressings for respectively delivering fluid to, and collecting fluidfrom, the wound, are formed by slots in and apertures through layerspermanently attached to each other in a stack.

Thus, in FIG. 10 a there is shown an exploded isometric view of an inletmanifold and outlet manifold stack (120) of five square coterminousthermoplastic polymer layers, being first to fifth layers (121) to(125), each attached with an adhesive film (not shown) or byheat-sealing to the adjacent layer in the stack (120).

The topmost (first) layer (121) (which is the most distal in thedressing in use) is a blank square capping layer.

The next (second) layer (122), shown in FIG. 10 b out of the manifoldstack (120), is a square layer, with an inlet manifold slot (126)through it. The slot (126) runs to one edge (127) of the layer (122) forconnection to a mating end of a fluid inlet tube ((not shown), andspreads into four adjacent branches (128) in a parallel array withspaces therebetween.

The next (third) layer (123) is another square layer, with inletmanifold apertures (129) through the layer (123) in an array such thatthe apertures (129) are in register with the inlet manifold slot (126)through the second layer (122) (shown in FIG. 10 b).

The next (fourth) layer (124), shown in FIG. 10 c out of the manifoldstack (120), is another square layer, with inlet manifold apertures(130) through the layer (124) in an array such that the apertures (130)are in register with the apertures (129) through the third layer (123).

It also has an outlet manifold slot (131) through it.

The slot (131) runs to one edge (132) of the layer (124) on the oppositeside of the manifold stack (120) from the edge (127) of the layer (122),for connection to a mating end of a fluid outlet tube (not shown).

It spreads into three adjacent branches (133) in a parallel array in thespaces between the apertures (130) in the layer (124) and in registerwith the spaces between the apertures (129) in the layer (122).

The final (fifth) layer (125) is another square layer, with inletmanifold apertures (134) through the layer (125) in an array such thatthe apertures (134) are in register with the inlet manifold apertures(130) through the fourth layer (124) (in turn in register with theapertures (129) through the third layer (123). It also has outletmanifold apertures (135) in the layer (125) in an array such that theapertures (135) are in register with the outlet manifold slot (131) inthe fourth layer (124).

It will be seen that, when the layers (121) to (125) are attachedtogether to form the stack (120), the topmost (first) layer (121), theinlet manifold slot (126) through the second layer (122), and the thirdlayer (123) cooperate to form an inlet manifold in the second layer(122), which is in use is connected to a mating end of a fluid inlettube (not shown).

The inlet manifold slot (126) through the second layer (122), and theinlet manifold apertures (129), (130) and (134) through the layers(123), (124) and (125), all being mutually in register, cooperate toform inlet manifold conduits though the third to fifth layers (123),(124) and (125) between the inlet manifold in the second layer (122) andthe proximal face (136) of the stack (120).

The third layer (121), the outlet manifold slot (131) through the fourthlayer (124), and the fifth layer (125) cooperate to form an outletmanifold in the fourth layer (124), which is in use is connected to amating end of a fluid outlet tube (not shown).

The outlet manifold slot (131) through the fourth layer (124), and theoutlet manifold apertures (135) through the fifth layer (125), beingmutually in register, cooperate to form outlet manifold conduits thoughthe fifth layer (125) between the outlet manifold in the fourth layer(124) and the proximal face (136) of the stack (120).

Referring to FIG. 11A, the apparatus (21) is a variant two-pump systemwith essentially identical, and identically numbered, components as inFIG. 2.

Thus, there is

-   a means for supply flow regulation, here a valve (14) in the fluid    supply tube (7) from the fluid reservoir (12), and-   a first device for moving fluid through the wound (5), here a    fixed-speed diaphragm pump (18A), e.g. preferably a small portable    diaphragm pump, acting not on the fluid aspiration tube (13), but on    an air aspiration tube (113) downstream of and away from an aspirate    collection vessel (19) to apply a low negative pressure on the wound    through the aspirate collection vessel (19); with-   a second device for moving fluid through the wound (5), here a    fixed-speed peristaltic pump (18B), e.g. preferably a small portable    peristaltic pump, applied to the irrigant in the fluid supply tube    (7) upstream of and towards the wound dressing,-   the first device (18A) and second device (18B), and the valve (14)    in the fluid supply tube (7), providing means for providing    simultaneous aspiration and irrigation of the wound (5), such that    fluid may be supplied to fill the flowpath from the fluid reservoir    via the fluid supply tube (via the means for supply flow regulation)    and moved by the devices through the flow path.

There is no means for aspirate flow regulation, e.g. a valve connectedto the fluid offtake tube (10).

Since first device (18A) and second device (18B) are fixed-speed, thevalve (14) in the fluid supply tube (7) provides the sole means forvarying the irrigant flow rate and the low negative pressure on thewound.

The following extra features are present:

The second device, the fixed-speed peristaltic pump (18B), is providedwith means for avoiding over-pressure, in the form of a bypass loop witha non-return valve (115). The loop runs from the fluid supply tube (7)downstream of the pump (18B) to a point in the fluid supply tube (7)upstream of the pump (18B).

A pressure monitor (116) connected to the fluid offtake tube (10) has afeedback connection to a bleed regulator, here a motorised rotary valve(117) on a bleed tube (118) running to and centrally penetrating the topof the aspirate collection vessel (19). This provides means for holdingthe low negative pressure on the wound at a steady level.

A filter (119) downstream of the aspirate collection vessel (19)prevents passage of gas- (often air-) borne particulates, includingliquids and micro-organisms, from the irrigant and/or exudate thatpasses into the aspirate collection vessel (19) into the first device(18A), whilst allowing the carrier gas to pass through the airaspiration tube (113) downstream of it to the first device (18A). Theoperation of the apparatus is as described herein before

Referring to FIG. 11B, this shows an alternative layout of theessentially identical, and identically numbered, components in FIG. 11Adownstream of point A in FIG. 11A. The bleed tube (118) runs to the airaspiration tube (113) downstream of the filter (119), rather than intothe aspirate collection vessel (19). This provides means for holding thelow negative pressure on the wound at a steady level. The operation ofthe apparatus is as described hereinbefore

Referring to FIG. 11C, this shows an alternative layout of theessentially identical, and identically numbered, components in FIG. 11Aupstream of point B in FIG. 11A. The second device (18B) is avariable-speed pump, and the valve (14) in the fluid supply tube (7) isomitted. The second device (18B) is the sole means for varying theirrigant flow rate and the low negative pressure on the wound. Theoperation of the apparatus is as described hereinbefore

Referring to FIG. 11D, this shows an alternative layout of theessentially identical, and identically numbered, components in FIG. 11Adownstream of point B in FIG. 11A.

The pressure monitor (116) is connected to a monitor offtake tube (120)and has a feedback connection to the bleed regulator, motorised rotaryvalve (117) on a bleed tube (118) running to the monitor offtake tube(120). This provides means for holding the low negative pressure on thewound at a steady level. The operation of the apparatus is as describedhereinbefore

Referring to FIG. 12A, this shows another alternative layout of theessentially identical, and identically numbered, components in FIG. 11Adownstream of point B in FIG. 11A.

The pressure monitor (116) is connected to a monitor offtake tube (120)and has a feedback connection to a means for aspirate flow regulation,here a motorised valve (16) in the air aspiration tube (113) downstreamof the filter (119).

This provides means for aspirate flow regulation and for holding the lownegative pressure on the wound at a steady level. The operation of theapparatus is as described hereinbefore

Referring to FIG. 12B, this shows another alternative layout of theessentially identical, and identically numbered, components in FIG. 12Adownstream of point B in FIG. 11A. The pressure monitor (116) isconnected to a monitor offtake tube (120) and has a feedback connectionto a means for aspirate flow regulation, here a motorised valve (16), inthe fluid offtake tube (10) upstream of the aspirate collection vessel(19).

This provides means for aspirate flow regulation and for holding the lownegative pressure on the wound at a steady level. The operation of theapparatus is as described hereinbefore

Referring to FIG. 12C, this shows another alternative layout of theessentially identical, and identically numbered, components in FIG. 12Adownstream of point B in FIG. 11A.

The pressure monitor (116) is connected to a monitor offtake tube (120)and has a feedback connection to a variable-speed first device (18A),here a variable-speed pump, downstream of the filter (119), and thevalve (16) in the fluid offtake tube (10) is omitted.

This provides means for aspirate flow regulation and for holding the lownegative pressure on the wound at a steady level. The operation of theapparatus is as described hereinbefore.

Referring to FIGS. 13 to 15, these forms of the dressing are providedwith a wound filler (348) under a circular backing layer (342).

This comprises respectively a generally downwardly domed or toroidal, oroblately spheroidal conformable hollow body, defined by a membrane (349)which is filled with a fluid, here air or nitrogen, that urges it to thewound shape.

The filler (348) is permanently attached to the backing layer via a boss(351), which is e.g. heat-sealed to the backing layer (342).

An inflation inlet pipe (350), inlet pipe (346) and outlet pipe (347)are mounted centrally in the boss (351) in the backing layer (342) abovethe hollow body (348). The inflation inlet pipe (350) communicates withthe interior of the hollow body (348), to permit inflation of the body(348). The inlet pipe (346) extends in a pipe (352) effectively throughthe hollow body (348). The outlet pipe (347) extends radiallyimmediately under the backing layer (342).

In FIG. 13, the pipe (352) communicates with an inlet manifold (353),formed by a membrane (361) with apertures (362) that is permanentlyattached to the filler (348) by heat-sealing.

It is filled with foam (363) formed of a suitable material, e.g. aresilient thermoplastic. Preferred materials include reticulatedfiltration polyurethane foams with small apertures or pores.

In FIG. 14, the outlet pipe (347) communicates with a layer of foam(364) formed of a suitable material, e.g. a resilient thermoplastic.Again, preferred materials include reticulated filtration polyurethanefoams with small apertures or pores.

In all of FIGS. 13, 14 and 15, in use, the pipe (346) ends in one ormore openings that deliver the irrigant fluid directly from the woundbed over an extended area.

Similarly, the outlet pipe (347) effectively collects the fluid radiallyfrom the wound periphery when the dressing is in use.

Referring to FIG. 16, the dressing is also provided with a wound filler(348) under a circular backing layer (342).

This also comprises a generally toroidal conformable hollow body,defined by a membrane (349) which is filled with a fluid, here air ornitrogen, that urges it to the wound shape.

The filler (348) may be permanently attached to the backing layer (342)via a first boss (351) and a layer of foam (364) formed of a suitablematerial, e.g. a resilient thermoplastic. Again, preferred materialsinclude reticulated filtration polyurethane foams with small aperturesor pores.

The first boss (351) and foam layer (364) are respectively heat-sealedto the backing layer (342) and the boss (351).

An inflation inlet pipe (350), inlet pipe (346) and outlet pipe (347)are mounted centrally in the first boss (351) in the backing layer (342)above the toroidal hollow body (348).

The inflation inlet pipe (350), inlet pipe (346) and outlet pipe (347)respectively each extend in a pipe (353), (354) and (355) through acentral tunnel (356) in the hollow body (348) to a second boss (357)attached to the toroidal hollow body (348).

The pipe (353) communicates with the interior of the hollow body (348),to permit inflation of the body (348).

The pipe (354) extends radially through the second boss (357) tocommunicate with an inlet manifold (352), formed by a membrane (361).

This is permanently attached to the filler (348) by heat-sealing in theform of a reticulated honeycomb with openings (362) that deliver theirrigant fluid directly to the wound bed over an extended area.

The pipe (355) collects the fluid flowing radially from the wound centrewhen the dressing is in use.

This form of the dressing is a more suitable layout for deeper wounds

In FIG. 17, the dressing is similar to that of FIG. 16, except that thetoroidal conformable hollow body, defined by a membrane (349), is filledwith a fluid, here a solid particulates, such as plastics crumbs orbeads, rather than a gas, such as air or an inert gas, such as nitrogenor argon. The inflation inlet pipe (350) and pipe (353) are omitted fromthe central tunnel (356).

Examples of contents for the body (348) also include gels, such assilicone gels or preferably cellulosic gels, for example hydrophiliccross-linked cellulosic gels, such as Intrasite™ cross-linked materials.Examples also include aerosol foams, and set aerosol foams, e.g.CaviCare™ foam.

Referring to FIGS. 18 and 19, another form for deeper wounds is shown.This comprises a circular backing layer (342) and a lobed chamber (363)in the form of a deeply indented disc much like a multiple Maltese crossor a stylised rose.

This is defined by an upper impervious membrane (361) and a lower porousfilm (362) with apertures (364) that deliver the irrigant fluid directlyfrom the wound bed over an extended area.

A number of configurations of the chamber (363) are shown, all of whichare able to conform well to the wound bed by the arms closing in andpossibly overlapping in insertion into the wound.

In a particular design of the chamber (363), shown lowermost, on of thearms extended and provided with an inlet port at the end of the extendedarm. This provides the opportunity for coupling and decoupling theirrigant supply remote from the dressing and the wound in use.

An inlet pipe (346) and outlet pipe (347) are mounted centrally in aboss (351) in the backing layer (342) above the chamber (363). The inletpipe (346) is permanently attached to, and communicate with the interiorof, the chamber (363), which thus effectively forms an inlet manifold.The space above the chamber (363) is filled with a loose gauze packing(364).

In FIG. 18, the outlet pipe (347) collects the fluid from the interiorof the dressing from just under the wound-facing face (343) of thebacking layer (342).

A variant of the dressing of FIG. 18 is shown in FIG. 19. The outletpipe (347) is mounted to open at the lowest point of the space above thechamber (363) into a piece of foam (374).

In FIG. 20, the dressing is similar to that of FIG. 13, except that theinlet pipe (352) communicates with an inlet manifold (353).

The latter is formed by a membrane (361) with apertures (362), over theupper surface of the generally downwardly domed wound hollow filler(348), rather than through it.

In FIG. 21, the dressing is similar to that of FIG. 14, with theaddition of an inlet manifold (353), formed by a membrane (361) withapertures (362), over the lower surface of the generally downwardlydomed annular wound hollow filler.

In FIG. 22, the generally downwardly domed annular wound hollow filleris omitted.

Referring to FIG. 23, another form for deeper wounds is shown. An inletpipe (346) and outlet pipe (347) are mounted centrally in a boss (351)in the backing layer (342) above a sealed-off foam filler (348).

The inlet pipe (346) is permanently attached to and passes through thefiller (348) to the wound bed. The outlet pipe (347) is attached to andcommunicates with the interior of, a chamber (363) defined by a porousfoam attached to the upper periphery of the filler (348). The chamber(363) thus effectively forms an outlet manifold.

In FIG. 24, the foam filler (348) is only partially sealed-off. Theinlet pipe (346) is permanently attached to and passes through thefiller (348) to the wound bed. The outlet pipe (347) is attached to andcommunicates with the interior of the foam of the filler (348). Fluidpasses into an annular gap (349) near the upper periphery of the filler(348) into the foam, which thus effectively forms an outlet manifold.

FIGS. 25 and 26 show dressings in which the inlet pipe (346) and outletpipe (347) pass through the backing layer (342).

In FIG. 25, they communicate with the interior of a porous bag filler(348) defined by a porous film (369) and filled with elasticallyresilient plastics bead or crumb.

In FIG. 26, they communicate with the wound space just below a foamfiller (348). The foam (348) may CaviCare™ foam, injected and formed insitu around the pipes (346) and (347).

Referring to FIG. 27, another form for deeper wounds is shown. Thiscomprises a circular, or more usually square or rectangular backinglayer (342) and a chamber (363) in the form of a deeply indented discmuch like a multiple Maltese cross or a stylised rose.

This is defined by an upper impervious membrane (361) and a lower porousfilm (362) with apertures (364) that deliver the irrigant fluid directlyto the wound bed over an extended area, and thus effectively forms aninlet manifold. Three configurations of the chamber (363) are shown inFIG. 27 b, all of which are able to conform well to the wound bed by thearms closing in and possibly overlapping in insertion into the wound.

The space above the chamber (363) is filled with a wound filler (348)under the backing layer (342). This comprises an oblately spheroidalconformable hollow body, defined by a membrane (349) that is filled witha fluid, here air or nitrogen, that urges it to the wound shape.

A moulded hat-shaped boss (351) is mounted centrally on the upperimpervious membrane (361) of the chamber (363). It has three internalchannels, conduits or passages through it (not shown), each with entryand exit apertures. The filler (348) is attached to the membrane (361)of the chamber (363) by adhesive, heat welding or a mechanical fixator,such as a cooperating pin and socket.

An inflation inlet pipe (350), inlet pipe (346) and outlet pipe (347)pass under the edge of the proximal face of the backing layer (342) ofthe dressing.

It extend radially immediately under the filler (348) and over themembrane (361) of the chamber (363) to each mate with an entry aperturein the boss (351).

An exit to the internal channel, conduit or passage through it thatreceives the inflation inlet pipe (350) communicates with the interiorof the hollow filler (348), to permit inflation.

An exit to the internal channel, conduit or passage that receives theinlet pipe (346) communicates with the interior of the chamber (363) todeliver the irrigant fluid via the chamber (363) to the wound bed overan extended area.

Similarly, an exit to the internal channel, conduit or passage thatreceives the outlet pipe (347) communicates with the space above thechamber (363) and under the wound filler (348), and collects flow ofirrigant and/or wound exudate radially from the wound periphery.

Referring to FIG. 28A, this shows another alternative layout of theessentially identical, and identically numbered, components in FIG. 12Cdownstream of point B in FIG. 12A, and alternative means for handlingthe aspirate flow to the aspirate collection vessel under negative orpositive pressure to the wound. The pressure monitor (116) is connectedto a monitor offtake tube (120) and has a feedback connection to avariable-speed first device (18A), here a variable-speed pump, upstreamof the aspirate collection vessel (19), and the filter (119) and the airaspiration tube (113) are omitted. This provides means for aspirate flowregulation and for holding the low negative pressure on the wound at asteady level. The operation of the apparatus is as describedhereinbefore.

Referring to FIG. 28B, this shows another alternative layout of theessentially identical, and identically numbered, components in FIG. 12Cdownstream of point B in FIG. 11A, and alternative means for handlingthe aspirate flow to the aspirate collection vessel under negative orpositive pressure to the wound. The pressure monitor (116) is omitted,as is the feedback connection to a variable-speed first device (18A),here a variable-speed pump, downstream of the aspirate collection vessel(19) and the filter (119).

A third device (18C), here a fixed-speed pump, provides means for movingfluid from the aspirate collection vessel (19) into a waste bag (12C).The operation of the apparatus is as described hereinbefore.

Referring to FIG. 29, this shows an alternative layout of theessentially identical, and identically numbered, components in FIG. 11Aupstream of point A in FIG. 11A.

It is a single-pump system essentially with the omission from theapparatus of FIG. 11A of the second device for moving irrigant fluidinto the wound dressing. The operation of the apparatus is as describedhereinbefore.

The use of the apparatus of the present invention will now be describedby way of example only in the following Example:

EXAMPLE 1 Removal of Wound Proteins and Derivatives with a Two-PumpApparatus

In this example, a gelatine sheet laid in a cavity wound modelrepresents wound proteins and derivatives to be removed by the two-pumpapparatus. The dressing is essentially identical with that in FIG. 18,i.e. it comprises a circular backing layer and a lobed chamber in theform of a deeply indented disc much like a multiple Maltese cross or astylised rose, defined by an upper impervious membrane and a lowerporous film with apertures that deliver the irrigant fluid directly fromthe wound bed over an extended area.

A two-pump system was set up essentially as in FIG. 2, with

-   an irrigant dispensing bottle—1000 ml Schott Duran, connected to a    peristaltic pump (Masterflex) for irrigant delivery, and associated    power supply and supply tube,-   a diaphragm vacuum pump (Schwarz) for aspiration, and associated    power supply and offtake tube, connected to-   a vacuum vessel (aspirate collection jar)—Nalgene 150 ml polystyrene    each pump being connected to-   a dressing consisting of the following elements:-   i) a wound contacting element, comprising a lobed bag with low    porosity ‘leaky’ membrane wound contact layer on the lower surface,    impermeable film on the top, and a foam spacer between the two    layers to allow free flow of irrigant solution.-   ii) a space filling element, comprising a reticulated, open-cell    foam (black reticulated foam, Foam Techniques) 30 mm thick, 60 mm    diameter-   iii) an occlusive adhesive coated polyurethane backing layer top    film (Smith & Nephew Medical) with acrylic pressure sensitive    adhesive-   iv) two tubes passing under the occlusive top film, and sealed to    prevent leakage of gas or liquid:    -   a. one tube centrally penetrating the top film of the        wound-contacting element to deliver irrigant into the chamber        formed by this film and the porous element;    -   b. the other tube of approximately equal length to remove        aspirate with the opening positioned just above the top film of        the wound contacting element.        Preparation of Gelatine Sheet:

A 20% aqueous solution of gelatine was prepared by weighing gelatineinto a glass jar and making it up to the required weight with deionisedwater. The jar was placed in an oven (Heraeus), at set temperature 85°C. After 60 minutes the jar was removed from the oven and shaken, toencourage mixing. Petri dishes were partially filled with 10 gquantities of the gelatine solution and placed in a fridge (LEC, settemperature: 4° C.) to set for at least 1 hour. Final thickness of thegelatine slab was 5 mm. Petri dishes containing the gelatine slabs wereremoved from the fridge at least 2 hours before use.

Preparation of Test Equipment and Materials

Irrigant solution (deionised water) and the Perspex wound model werepre-conditioned in an oven (Gallenkamp) at set temperature 37° C., forat least 4 hours before use.

For each test, a freshly prepared gelatine slab was removed from a Petridish and weighed.

The Perspex wound model was then removed from the oven and the gelatineslab placed at the bottom of the cavity. Application of the dressing tothe wound model was as follows:

-   -   the wound contacting element was carefully placed over the        gelatine slab    -   the foam filler was placed on top of this with the irrigant and        aspirate tubes running centrally to the top of the cavity (the        foam filler was slit to the centre to facilitate this).    -   the side entry port, pre-threaded onto the tubes, was adhesively        bonded to the upper surface of the wound model block using an        acrylic pressure sensitive adhesive    -   the top adhesive coated film was applied over all of the        elements and pressed down to give a seal on all sides, and        especially around the tube entry/exit point

Application of the dressing to the wound model was the same for alltests performed. All tubing used was the same for each experiment (e.g.material, diameter, length).

Simultaneous Irrigation & Aspiration

A schematic diagram of the system used in the experiment is shown below.For the experiment most of the apparatus (not including the pumps, powersupply, and connecting tubing to and from the pumps) was placed in anoven (Gallenkamp, set temperature: 37° C.), on the same shelf.

Before starting the irrigation pump a vacuum was drawn on the system tocheck that the dressing and tube connections were substantially airtight(the pumping system was controlled to give a pressure at the vacuumvessel of approximately −75 mmHg before opening the system up to includethe dressing).

Once system integrity had been confirmed, the irrigation pump wasstarted (nominal flow rate: 50 ml/hr), i.e. both pumps running together.Timing of the experiment was started when the advancing water frontwithin the irrigant tube was observed to have reached the top of thedressing.

After 60 minutes, the irrigation pump was stopped, shortly followed bythe vacuum (aspiration) pump.

Aspirate liquid collected in the vacuum jar was decanted into a glassjar. The vacuum jar was rinsed with ˜100 ml of deionised water and thisadded to the same glass jar.

The aspirate solution was placed in an oven (Heraeus, set temperature:130° C.) and dried to constant weight.

Sequential Irrigation & Aspiration

The experimental set up was as for the simultaneousirrigation/aspiration experiment.

Before starting the experiment a vacuum was pulled on the system tocheck that the dressing and tube connections were substantiallyairtight. The pumping system was controlled to give a pressure at thevacuum vessel of approximately −75 mmHg before opening the system up toinclude the dressing. Once system integrity had been confirmed, theirrigation pump was started (nominal rate: 186 ml/hr) and run until theadvancing water front in the irrigant tube was observed to have reachedthe top of the dressing. The pump was temporarily stopped at this pointwhilst the vacuum line was sealed (using a tube clamp) and the vacuumpump stopped.

Timing of the experiment was from the point the irrigation pump wasrestarted. The pump was run until 50 ml of irrigant had entered thewound model (just over 16 minutes at the rate of 186 ml/hr). At thispoint the irrigant pump was stopped.

It was observed that during the filling phase of sequential filling andflushing, air trapped in the model wound cavity caused the top film ofthe dressing to inflate substantially, to a point approaching failure.

After a further ˜44 minutes (60 minutes from the start of theexperiment) the vacuum pump was started and the tube clamp on theaspirate line removed. The wound model was aspirated for 5 minutes.Towards the end of this period a small leak was introduced into the topfilm of the dressing to maximise the amount of fluid drawn from thewound model (it was observed that as the pressure differential betweenthe wound model cavity and the vacuum jar reduced to zero, the flow ofaspirate also tended to slow. Introducing a small leak re-establishedthe pressure differential and the flow of aspirate out of the cavity).

Results

Simultaneous Irrigation & Aspiration Reference Aspirate Recovery ofConcentration of gelatine in number recovered (g) gelatine (%) aspiratedfluid (% w/w) 1 48.81 79.33 3.27 2 45.64 72.30 3.18 3 48.84 68.05 2.76Mean 47.76 73.22 3.07

Sequential Irrigation & Aspiration Cycle Reference Aspirate Recovery ofConcentration of gelatine in number recovered (g) gelatine (%) aspiratedfluid (% w/w) 1 32.08 19.59 1.23 2 34.09 18.35 1.07 3 33.90 10.77 0.64Mean 33.36 16.24 0.98Conclusions

Simultaneously irrigating and aspirating the wound model removed more ofthe gelatine placed at the base of the wound model cavity thansequentially filling and emptying the cavity, even though the amount ofliquid entering the wound and the duration of the experiment were thesame in both cases. Simultaneously irrigating and aspirating alsoremoved more fluid from the model wound.

EXAMPLE 2 The Combination of Simultaneous Fluid Flow (Irrigation) andAspiration (Under Reduced Pressure) on Wound Bed Fibroblasts Comparedwith the Exposure of Wound Bed Fibroblasts to Repeated Fill-Empty Cyclesof Fluid Flow and Aspiration

An apparatus of the present invention was constructed essentially as inFIG. 30, which is an apparatus where an irrigant is deliveredcontinually to the wound bed and the resultant wound exudate/fluidmixture is at the same time continually aspirated from the wound.Alternative systems are known where the wound is subjected to repeatediteration of a cycle of fluid delivery followed by a period ofaspiration under reduced pressure.

The apparatus comprised a surrogate wound chamber (Minucells perfusionchamber) in which normal diploid human fibroblasts were cultured on 13mm diameter (Thermanox polymer) cover slips retained in a two partsupport (Minucells Minusheets). Tissues present in the healing woundthat must survive and proliferate were represented by the cells withinthe chamber. Nutrient medium (DMEM with 10% FCS with 1% Buffer All) tosimulate an irrigant fluid/wound exudate mixture, was pumped from areservoir into the lower aspect of the chamber where it bathed thefibroblasts and was removed from the upper aspect of the chamber andreturned to a second reservoir. The wound chamber was maintained at lessthan atmospheric pressure by means of a vacuum pump in line with thecircuit.

The pumps for the circuit were peristaltic pumps acting on silicone (orequivalent) elastic tubing. The circuit was exposed to a vacuum of nomore than 10% atmospheric pressure, 950 mbar and atmospheric pressurevaried up to a maximum value of 1044 mbar. The internal diameter of thetubing was 1.0 mm. A total volume for the circuit including the chamberand the reservoir of between 50 and 220 ml was used. The flow rates usedwere at a number of values between 0.1 ml min⁻¹ and 2.0 ml⁻¹ min⁻¹.

An experiment was conducted that simulated conditions that are notuncommon for healing wounds whereby a fluid was delivered to the woundbed and the application of a vacuum was used to remove the mixture offluid and exudate to a waste reservoir.

An air bleed fluid control valve was additionally positioned in thecircuit so that on opening the air bleed occurred for a time and closedthe fluid flow, the simulated irrigant fluid/wound exudate mixture wasevacuated from the chamber and the fibroblasts were maintained under anegative pressure relative to the atmosphere. This represents anempty/fill system.

Results and Conclusions

The following results were obtained for a circuit comprising a woundchamber as above containing a total volume of nutrient media (154 ml)pumped at a flow rate of 0.2 ml min⁻¹ and where vacuum was set at 950mbar and where atmospheric pressure varied up to a maximum value of 1044mbar. The wound chamber and media were held at 37° C. for 25 hours. Inone set of wound chambers continuous flow was maintained. In a secondset of chambers 6 cycles of empty/fill were performed with each fill orempty phase lasting 1 hour.

In controls where empty/fill system with 6× cycles of 1 hour empty/1hour fill over a total of 25 hours, the survival and growth of thefibroblasts is inhibited.

However, when the nutrient medium flow in the first circuit is deliveredcontinually to the Minucells chamber and the resultant nutrient mediumis at the same time continually aspirated from the Minucells chamberunder vacuum was set at 950 mbar and where atmospheric pressure variedup to a maximum value of 1044 mbar, the fibroblasts survive andproliferate to a greater extent during a 25 hour period than the controlempty/fill circuits

Mean relative level of cell activity* after 25 Conditions hours.Baseline cell activity prior to 100% introduction to wound chamber Fillempty 6 cycles 93% Continuous flow 143% *Cell activity measured with aWST (Tetrazolium based mitochondrial dehdrogenase activity assay). Datanormalised to fibroblasts seeded onto coverslips with normal nutrientmedia baseline activity

The combination of continuous fluid flow at 0.2 ml min⁻¹ and waste fluidremoval under vacuum of no more than 10% atmospheric pressure, 950 mbarand atmospheric pressure varied up to a maximum value of 1044 mbar,enhances the cell response necessary for wound healing more than thefill empty fill pattern under vacuum.

1. A method of treating a wound to promote wound healing, the methodcomprising: providing a fluid flow path, the fluid flow path comprisinga conformable wound dressing, having a backing layer forming afluid-tight seal over a wound, the backing layer comprising awound-facing face, a fluid supply tube, and a fluid offtake tube; movingfluid from a fluid reservoir through the fluid flow path; regulating theamount of fluid that flows through the fluid supply tube; and regulatingthe amount of fluid that flows through the fluid offtake tube; whereinfluid is moved through the fluid flow path to provide simultaneousaspiration and irrigation to the wound; and wherein fluid moving throughthe fluid flow path is regulated to hold negative pressure on the woundat a steady level while providing simultaneous aspiration and irrigationto the wound.
 2. The method of claim 1, wherein both regulating theamount of fluid that flows through the fluid supply tube and regulatingthe amount of fluid that flows through the fluid offtake tube compriseregulating the amount of fluid with a pump.
 3. The method of claim 1,wherein at least one of regulating the amount of fluid that flowsthrough the fluid supply tube and regulating the amount of fluid thatflows through the fluid offtake tube comprises regulating the amount offluid with a variable speed pump.
 4. The method of claim 1, wherein atleast one of regulating the amount of fluid that flows through the fluidsupply tube and regulating the amount of fluid that flows through thefluid offtake tube comprises regulating the amount of fluid with aregulator.
 5. The method of claim 4, wherein the regulator is a valve.6. The method of claim 1, wherein regulating fluid moving through thefluid flow path to hold negative pressure on the wound at a steady levelwhile providing simultaneous aspiration and irrigation to the woundcomprises monitoring negative pressure under the backing layer.
 7. Themethod of claim 6, further comprising adjusting negative pressure inresponse to monitoring negative pressure under the backing layer.
 8. Themethod of claim 6, wherein the negative pressure is monitored under thebacking layer with a pressure monitor connected to a monitor offtaketube.
 9. The method of claim 8, further comprising regulating the amountof fluid that flows through the fluid offtake tube by operating a bleedregulator on a bleed tube connected to the monitor offtake tube.
 10. Themethod of claim 1, wherein regulating the amount of fluid that flowsthrough the fluid offtake tube comprises operating a bleed regulatorconnected to the fluid flow path.
 11. The method of claim 1, whereinregulating the amount of fluid that flows through the fluid supply tubeis independent of regulating the amount of fluid that flows through thefluid offtake tube.
 12. An apparatus for aspirating, irrigating and/orcleansing wounds, comprising: a backing layer capable of forming afluid-tight seal over a wound; a fluid supply tube arranged to providefluid from a fluid reservoir to the wound; a fluid offtake tube arrangedto withdraw fluid from the wound; a pump in communication with at leastone of the fluid supply tube and the fluid offtake tube and configuredto move fluid through at least one of the fluid supply tube and thefluid offtake tube; a bleed regulator on a bleed tube connected to amonitor offtake tube, the bleed regulator in communication with thefluid offtake tube and configured to regulate the rate of fluid thatflows through the fluid offtake tube; and a pressure monitor connectedto the monitor offtake tube and configured to monitor negative pressureunder the backing layer; wherein the apparatus is configured to providesimultaneous aspiration and irrigation to the wound such that fluid maybe supplied to the wound from the fluid reservoir via the fluid supplytube while fluid is aspirated through the fluid offtake tube; andwherein, based on the monitored negative pressure, the bleed regulatoris configured to hold negative pressure on the wound at a steady levelwhile simultaneous aspiration and irrigation is provided to the wound.13. The apparatus of claim 12, wherein the bleed regulator is a valve.14. The apparatus of claim 12, wherein the pump is in communication withthe fluid supply tube and is configured to move fluid through the fluidsupply tube.
 15. The apparatus of claim 12, wherein the bleed regulatorcomprises a valve configured to vent the wound from atmosphere.
 16. Theapparatus of claim 12, further comprising a non-return valve incommunication with the fluid supply tube and configured to avoidoverpressure on the wound.